diff --git a/CHANGELOG.md b/CHANGELOG.md
index b16abb0c..9a3dbaca 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Added
+- Add return types in the test suite ([#748](https://github.com/jsonrainbow/json-schema/pull/748))
+
 ### Fixed
 - Correct misconfigured mocks in JsonSchema\Tests\Uri\UriRetrieverTest ([#741](https://github.com/jsonrainbow/json-schema/pull/741))
 - Fix pugx badges in README ([#742](https://github.com/jsonrainbow/json-schema/pull/742))
diff --git a/tests/ConstraintErrorTest.php b/tests/ConstraintErrorTest.php
index 487f7d2a..158f3074 100644
--- a/tests/ConstraintErrorTest.php
+++ b/tests/ConstraintErrorTest.php
@@ -14,13 +14,13 @@
 
 class ConstraintErrorTest extends TestCase
 {
-    public function testGetValidMessage()
+    public function testGetValidMessage(): void
     {
         $e = ConstraintError::ALL_OF();
         $this->assertEquals('Failed to match all schemas', $e->getMessage());
     }
 
-    public function testGetInvalidMessage()
+    public function testGetInvalidMessage(): void
     {
         $e = ConstraintError::MISSING_ERROR();
 
diff --git a/tests/Constraints/AdditionalPropertiesTest.php b/tests/Constraints/AdditionalPropertiesTest.php
index d5db24fb..82b31971 100644
--- a/tests/Constraints/AdditionalPropertiesTest.php
+++ b/tests/Constraints/AdditionalPropertiesTest.php
@@ -15,7 +15,7 @@ class AdditionalPropertiesTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -114,7 +114,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/ArraysTest.php b/tests/Constraints/ArraysTest.php
index 1d4d08bd..4b2eb576 100644
--- a/tests/Constraints/ArraysTest.php
+++ b/tests/Constraints/ArraysTest.php
@@ -13,7 +13,7 @@ class ArraysTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -120,7 +120,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/BaseTestCase.php b/tests/Constraints/BaseTestCase.php
index 21972c58..ba55b461 100644
--- a/tests/Constraints/BaseTestCase.php
+++ b/tests/Constraints/BaseTestCase.php
@@ -26,7 +26,7 @@ abstract class BaseTestCase extends VeryBaseTestCase
     /**
      * @dataProvider getInvalidTests
      */
-    public function testInvalidCases($input, $schema, $checkMode = Constraint::CHECK_MODE_NORMAL, $errors = [])
+    public function testInvalidCases($input, $schema, $checkMode = Constraint::CHECK_MODE_NORMAL, $errors = []): void
     {
         $checkMode = $checkMode === null ? Constraint::CHECK_MODE_NORMAL : $checkMode;
         if ($this->validateSchema) {
@@ -55,7 +55,7 @@ public function testInvalidCases($input, $schema, $checkMode = Constraint::CHECK
     /**
      * @dataProvider getInvalidForAssocTests
      */
-    public function testInvalidCasesUsingAssoc($input, $schema, $checkMode = Constraint::CHECK_MODE_TYPE_CAST, $errors = [])
+    public function testInvalidCasesUsingAssoc($input, $schema, $checkMode = Constraint::CHECK_MODE_TYPE_CAST, $errors = []): void
     {
         $checkMode = $checkMode === null ? Constraint::CHECK_MODE_TYPE_CAST : $checkMode;
         if ($this->validateSchema) {
@@ -87,7 +87,7 @@ public function testInvalidCasesUsingAssoc($input, $schema, $checkMode = Constra
     /**
      * @dataProvider getValidTests
      */
-    public function testValidCases($input, $schema, $checkMode = Constraint::CHECK_MODE_NORMAL)
+    public function testValidCases($input, $schema, $checkMode = Constraint::CHECK_MODE_NORMAL): void
     {
         if ($this->validateSchema) {
             $checkMode |= Constraint::CHECK_MODE_VALIDATE_SCHEMA;
@@ -109,7 +109,7 @@ public function testValidCases($input, $schema, $checkMode = Constraint::CHECK_M
     /**
      * @dataProvider getValidForAssocTests
      */
-    public function testValidCasesUsingAssoc($input, $schema, $checkMode = Constraint::CHECK_MODE_TYPE_CAST)
+    public function testValidCasesUsingAssoc($input, $schema, $checkMode = Constraint::CHECK_MODE_TYPE_CAST): void
     {
         if ($this->validateSchema) {
             $checkMode |= Constraint::CHECK_MODE_VALIDATE_SCHEMA;
@@ -133,28 +133,16 @@ public function testValidCasesUsingAssoc($input, $schema, $checkMode = Constrain
         $this->assertTrue($validator->isValid(), print_r($validator->getErrors(), true));
     }
 
-    /**
-     * @return array[]
-     */
-    abstract public function getValidTests();
+    abstract public function getValidTests(): array;
 
-    /**
-     * @return array[]
-     */
-    public function getValidForAssocTests()
+    public function getValidForAssocTests(): array
     {
         return $this->getValidTests();
     }
 
-    /**
-     * @return array[]
-     */
-    abstract public function getInvalidTests();
+    abstract public function getInvalidTests(): array;
 
-    /**
-     * @return array[]
-     */
-    public function getInvalidForAssocTests()
+    public function getInvalidForAssocTests(): array
     {
         return $this->getInvalidTests();
     }
diff --git a/tests/Constraints/BasicTypesTest.php b/tests/Constraints/BasicTypesTest.php
index c238dba3..01e1f7ba 100644
--- a/tests/Constraints/BasicTypesTest.php
+++ b/tests/Constraints/BasicTypesTest.php
@@ -14,7 +14,7 @@ class BasicTypesTest extends BaseTestCase
     protected $schemaSpec = 'http://json-schema.org/draft-03/schema#';
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -104,7 +104,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/CoerciveTest.php b/tests/Constraints/CoerciveTest.php
index 1f8670cf..3c028ba0 100644
--- a/tests/Constraints/CoerciveTest.php
+++ b/tests/Constraints/CoerciveTest.php
@@ -24,7 +24,7 @@ public function setUp(): void
         $this->factory->setConfig(Constraint::CHECK_MODE_TYPE_CAST | Constraint::CHECK_MODE_COERCE_TYPES);
     }
 
-    public function dataCoerceCases()
+    public function dataCoerceCases(): array
     {
         // check type conversions
         $types = [
@@ -190,7 +190,7 @@ public function dataCoerceCases()
     }
 
     /** @dataProvider dataCoerceCases **/
-    public function testCoerceCases($schema, $data, $startType, $endType, $endValue, $valid, $extraFlags = 0, $assoc = false)
+    public function testCoerceCases($schema, $data, $startType, $endType, $endValue, $valid, $extraFlags = 0, $assoc = false): void
     {
         $validator = new Validator($this->factory);
 
@@ -232,12 +232,12 @@ public function testCoerceCases($schema, $data, $startType, $endType, $endValue,
     }
 
     /** @dataProvider dataCoerceCases **/
-    public function testCoerceCasesUsingAssoc($schema, $data, $startType, $endType, $endValue, $valid, $early = false)
+    public function testCoerceCasesUsingAssoc($schema, $data, $startType, $endType, $endValue, $valid, $early = false): void
     {
         $this->testCoerceCases($schema, $data, $startType, $endType, $endValue, $valid, $early, true);
     }
 
-    public function testCoerceAPI()
+    public function testCoerceAPI(): void
     {
         $input = json_decode('{"propertyOne": "10"}');
         $schema = json_decode('{"properties":{"propertyOne":{"type":"number"}}}');
diff --git a/tests/Constraints/ConstTest.php b/tests/Constraints/ConstTest.php
index bcd8b966..6b4cfc1f 100644
--- a/tests/Constraints/ConstTest.php
+++ b/tests/Constraints/ConstTest.php
@@ -14,7 +14,7 @@ class ConstTest extends BaseTestCase
     protected $schemaSpec = 'http://json-schema.org/draft-06/schema#';
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -68,7 +68,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/DefaultPropertiesTest.php b/tests/Constraints/DefaultPropertiesTest.php
index 95dde8e9..28498352 100644
--- a/tests/Constraints/DefaultPropertiesTest.php
+++ b/tests/Constraints/DefaultPropertiesTest.php
@@ -16,7 +16,7 @@
 
 class DefaultPropertiesTest extends VeryBaseTestCase
 {
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             /*
@@ -170,7 +170,7 @@ public function getValidTests()
     /**
      * @dataProvider getValidTests
      */
-    public function testValidCases($input, $schema, $expectOutput = null, $checkMode = 0)
+    public function testValidCases($input, $schema, $expectOutput = null, $checkMode = 0): void
     {
         if (is_string($input)) {
             $inputDecoded = json_decode($input);
@@ -197,7 +197,7 @@ public function testValidCases($input, $schema, $expectOutput = null, $checkMode
     /**
      * @dataProvider getValidTests
      */
-    public function testValidCasesUsingAssoc($input, $schema, $expectOutput = null, $checkMode = 0)
+    public function testValidCasesUsingAssoc($input, $schema, $expectOutput = null, $checkMode = 0): void
     {
         $input = json_decode($input, true);
 
@@ -208,14 +208,14 @@ public function testValidCasesUsingAssoc($input, $schema, $expectOutput = null,
     /**
      * @dataProvider getValidTests
      */
-    public function testValidCasesUsingAssocWithoutTypeCast($input, $schema, $expectOutput = null, $checkMode = 0)
+    public function testValidCasesUsingAssocWithoutTypeCast($input, $schema, $expectOutput = null, $checkMode = 0): void
     {
         $input = json_decode($input, true);
 
         self::testValidCases($input, $schema, $expectOutput, $checkMode);
     }
 
-    public function testNoModificationViaReferences()
+    public function testNoModificationViaReferences(): void
     {
         $input = json_decode('{}');
         $schema = json_decode('{"properties":{"propertyOne":{"default":"valueOne"}}}');
@@ -229,7 +229,7 @@ public function testNoModificationViaReferences()
         $this->assertEquals('valueOne', $schema->properties->propertyOne->default);
     }
 
-    public function testLeaveBasicTypesAlone()
+    public function testLeaveBasicTypesAlone(): void
     {
         $input = json_decode('"ThisIsAString"');
         $schema = json_decode('{"properties": {"propertyOne": {"default": "valueOne"}}}');
diff --git a/tests/Constraints/DependenciesTest.php b/tests/Constraints/DependenciesTest.php
index 38483f88..ff3ffb8e 100644
--- a/tests/Constraints/DependenciesTest.php
+++ b/tests/Constraints/DependenciesTest.php
@@ -14,7 +14,7 @@ class DependenciesTest extends BaseTestCase
     protected $schemaSpec = 'http://json-schema.org/draft-03/schema#';
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -80,7 +80,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/DisallowTest.php b/tests/Constraints/DisallowTest.php
index 6a61dcea..1fe93f6c 100644
--- a/tests/Constraints/DisallowTest.php
+++ b/tests/Constraints/DisallowTest.php
@@ -19,7 +19,7 @@ class DisallowTest extends BaseTestCase
     protected $schemaSpec = 'http://json-schema.org/draft-03/schema#';
     protected $validateSchema = false;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -107,7 +107,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/DivisibleByTest.php b/tests/Constraints/DivisibleByTest.php
index e08e2b9d..354d6a29 100644
--- a/tests/Constraints/DivisibleByTest.php
+++ b/tests/Constraints/DivisibleByTest.php
@@ -13,7 +13,7 @@ class DivisibleByTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -55,7 +55,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/EnumTest.php b/tests/Constraints/EnumTest.php
index 8b7a7d51..2ff14147 100644
--- a/tests/Constraints/EnumTest.php
+++ b/tests/Constraints/EnumTest.php
@@ -14,7 +14,7 @@ class EnumTest extends BaseTestCase
     protected $schemaSpec = 'http://json-schema.org/draft-03/schema#';
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -94,7 +94,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/ExtendsTest.php b/tests/Constraints/ExtendsTest.php
index ee53ed84..286b24b8 100644
--- a/tests/Constraints/ExtendsTest.php
+++ b/tests/Constraints/ExtendsTest.php
@@ -14,7 +14,7 @@ class ExtendsTest extends BaseTestCase
     protected $schemaSpec = 'http://json-schema.org/draft-03/schema#';
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -93,7 +93,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/FactoryTest.php b/tests/Constraints/FactoryTest.php
index 451fa94d..f29614ee 100644
--- a/tests/Constraints/FactoryTest.php
+++ b/tests/Constraints/FactoryTest.php
@@ -53,7 +53,7 @@ protected function setUp(): void
      * @param string $constraintName
      * @param string $expectedClass
      */
-    public function testCreateInstanceForConstraintName($constraintName, $expectedClass)
+    public function testCreateInstanceForConstraintName($constraintName, $expectedClass): void
     {
         $constraint = $this->factory->createInstanceFor($constraintName);
 
@@ -61,7 +61,7 @@ public function testCreateInstanceForConstraintName($constraintName, $expectedCl
         $this->assertInstanceOf('JsonSchema\Constraints\ConstraintInterface', $constraint);
     }
 
-    public function constraintNameProvider()
+    public function constraintNameProvider(): array
     {
         return [
             ['array', 'JsonSchema\Constraints\CollectionConstraint'],
@@ -83,34 +83,34 @@ public function constraintNameProvider()
      *
      * @param string $constraintName
      */
-    public function testExceptionWhenCreateInstanceForInvalidConstraintName($constraintName)
+    public function testExceptionWhenCreateInstanceForInvalidConstraintName($constraintName): void
     {
         $this->expectException('JsonSchema\Exception\InvalidArgumentException');
         $this->factory->createInstanceFor($constraintName);
     }
 
-    public function invalidConstraintNameProvider()
+    public function invalidConstraintNameProvider(): array
     {
         return [
             ['invalidConstraintName'],
         ];
     }
 
-    public function testSetConstraintClassExistsCondition()
+    public function testSetConstraintClassExistsCondition(): void
     {
         $this->expectException(\JsonSchema\Exception\InvalidArgumentException::class);
 
         $this->factory->setConstraintClass('string', 'SomeConstraint');
     }
 
-    public function testSetConstraintClassImplementsCondition()
+    public function testSetConstraintClassImplementsCondition(): void
     {
         $this->expectException(\JsonSchema\Exception\InvalidArgumentException::class);
 
         $this->factory->setConstraintClass('string', 'JsonSchema\Tests\Constraints\MyBadConstraint');
     }
 
-    public function testSetConstraintClassInstance()
+    public function testSetConstraintClassInstance(): void
     {
         $this->factory->setConstraintClass('string', 'JsonSchema\Tests\Constraints\MyStringConstraint');
         $constraint = $this->factory->createInstanceFor('string');
@@ -118,7 +118,7 @@ public function testSetConstraintClassInstance()
         $this->assertInstanceOf('JsonSchema\Constraints\ConstraintInterface', $constraint);
     }
 
-    public function testCheckMode()
+    public function testCheckMode(): void
     {
         $f = new Factory();
 
diff --git a/tests/Constraints/FormatTest.php b/tests/Constraints/FormatTest.php
index bb511607..2d91e5fe 100644
--- a/tests/Constraints/FormatTest.php
+++ b/tests/Constraints/FormatTest.php
@@ -22,7 +22,7 @@ public function setUp(): void
         date_default_timezone_set('UTC');
     }
 
-    public function testNullThing()
+    public function testNullThing(): void
     {
         $validator = new FormatConstraint();
         $schema = new \stdClass();
@@ -32,7 +32,7 @@ public function testNullThing()
         $this->assertEmpty($validator->getErrors());
     }
 
-    public function testRegex()
+    public function testRegex(): void
     {
         $validator = new FormatConstraint();
         $schema = new \stdClass();
@@ -57,7 +57,7 @@ public function testRegex()
     /**
      * @dataProvider getValidFormats
      */
-    public function testValidFormat($string, $format)
+    public function testValidFormat($string, $format): void
     {
         $validator = new FormatConstraint();
         $schema = new \stdClass();
@@ -70,7 +70,7 @@ public function testValidFormat($string, $format)
     /**
      * @dataProvider getInvalidFormats
      */
-    public function testInvalidFormat($string, $format)
+    public function testInvalidFormat($string, $format): void
     {
         $validator = new FormatConstraint();
         $schema = new \stdClass();
@@ -83,7 +83,7 @@ public function testInvalidFormat($string, $format)
     /**
      * @dataProvider getInvalidFormats
      */
-    public function testDisabledFormat($string, $format)
+    public function testDisabledFormat($string, $format): void
     {
         $factory = new Factory();
         $validator = new FormatConstraint($factory);
@@ -95,7 +95,7 @@ public function testDisabledFormat($string, $format)
         $this->assertEmpty($validator->getErrors());
     }
 
-    public function getValidFormats()
+    public function getValidFormats(): array
     {
         return [
             ['2001-01-23', 'date'],
@@ -167,7 +167,7 @@ public function getValidFormats()
         ];
     }
 
-    public function getInvalidFormats()
+    public function getInvalidFormats(): array
     {
         return [
             ['January 1st, 1910', 'date'],
@@ -218,7 +218,7 @@ public function getInvalidFormats()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
@@ -236,7 +236,7 @@ public function getValidTests()
         ];
     }
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/LongArraysTest.php b/tests/Constraints/LongArraysTest.php
index 862b4e3b..8b8c88f0 100644
--- a/tests/Constraints/LongArraysTest.php
+++ b/tests/Constraints/LongArraysTest.php
@@ -17,7 +17,7 @@ class LongArraysTest extends VeryBaseTestCase
 {
     protected $validateSchema = true;
 
-    public function testLongStringArray()
+    public function testLongStringArray(): void
     {
         $schema =
             '{
@@ -45,7 +45,7 @@ public function testLongStringArray()
         $this->assertTrue($validator->isValid(), print_r($validator->getErrors(), true));
     }
 
-    public function testLongNumberArray()
+    public function testLongNumberArray(): void
     {
         $schema =
             '{
@@ -73,7 +73,7 @@ public function testLongNumberArray()
         $this->assertTrue($validator->isValid(), print_r($validator->getErrors(), true));
     }
 
-    public function testLongIntegerArray()
+    public function testLongIntegerArray(): void
     {
         $schema =
             '{
diff --git a/tests/Constraints/MinItemsMaxItemsTest.php b/tests/Constraints/MinItemsMaxItemsTest.php
index 477eb609..f07bcd6f 100644
--- a/tests/Constraints/MinItemsMaxItemsTest.php
+++ b/tests/Constraints/MinItemsMaxItemsTest.php
@@ -13,7 +13,7 @@ class MinItemsMaxItemsTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -41,7 +41,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/MinLengthMaxLengthMultiByteTest.php b/tests/Constraints/MinLengthMaxLengthMultiByteTest.php
index 2b8b6ca7..ab6db1a3 100644
--- a/tests/Constraints/MinLengthMaxLengthMultiByteTest.php
+++ b/tests/Constraints/MinLengthMaxLengthMultiByteTest.php
@@ -20,7 +20,7 @@ protected function setUp(): void
         }
     }
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -48,7 +48,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/MinLengthMaxLengthTest.php b/tests/Constraints/MinLengthMaxLengthTest.php
index 78d27abb..4832dfd5 100644
--- a/tests/Constraints/MinLengthMaxLengthTest.php
+++ b/tests/Constraints/MinLengthMaxLengthTest.php
@@ -13,7 +13,7 @@ class MinLengthMaxLengthTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -41,7 +41,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/MinMaxPropertiesTest.php b/tests/Constraints/MinMaxPropertiesTest.php
index 763b80e0..bf3a3182 100644
--- a/tests/Constraints/MinMaxPropertiesTest.php
+++ b/tests/Constraints/MinMaxPropertiesTest.php
@@ -16,7 +16,7 @@ class MinMaxPropertiesTest extends BaseTestCase
     /**
      * {@inheritdoc}
      */
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
@@ -69,7 +69,7 @@ public function getValidTests()
     /**
      * {@inheritdoc}
      */
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/MinimumMaximumTest.php b/tests/Constraints/MinimumMaximumTest.php
index ab02bfd0..6f66565b 100644
--- a/tests/Constraints/MinimumMaximumTest.php
+++ b/tests/Constraints/MinimumMaximumTest.php
@@ -13,7 +13,7 @@ class MinimumMaximumTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -110,7 +110,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/NotTest.php b/tests/Constraints/NotTest.php
index 092b2e39..2b6b48e3 100644
--- a/tests/Constraints/NotTest.php
+++ b/tests/Constraints/NotTest.php
@@ -13,7 +13,7 @@ class NotTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -49,7 +49,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/NumberAndIntegerTypesTest.php b/tests/Constraints/NumberAndIntegerTypesTest.php
index 79216a24..78b02110 100644
--- a/tests/Constraints/NumberAndIntegerTypesTest.php
+++ b/tests/Constraints/NumberAndIntegerTypesTest.php
@@ -13,7 +13,7 @@ class NumberAndIntegerTypesTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -57,7 +57,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/OfPropertiesTest.php b/tests/Constraints/OfPropertiesTest.php
index ac31db92..b602c0b4 100644
--- a/tests/Constraints/OfPropertiesTest.php
+++ b/tests/Constraints/OfPropertiesTest.php
@@ -18,7 +18,7 @@ class OfPropertiesTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
@@ -56,7 +56,7 @@ public function getValidTests()
         ];
     }
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -232,7 +232,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function testNoPrematureAnyOfException()
+    public function testNoPrematureAnyOfException(): void
     {
         $schema = json_decode('{
             "type": "object",
@@ -252,7 +252,7 @@ public function testNoPrematureAnyOfException()
         $this->assertTrue($v->isValid());
     }
 
-    public function testNoPrematureOneOfException()
+    public function testNoPrematureOneOfException(): void
     {
         $schema = json_decode('{
             "type": "object",
diff --git a/tests/Constraints/PatternPropertiesTest.php b/tests/Constraints/PatternPropertiesTest.php
index 0672fb01..526777ef 100644
--- a/tests/Constraints/PatternPropertiesTest.php
+++ b/tests/Constraints/PatternPropertiesTest.php
@@ -13,7 +13,7 @@ class PatternPropertiesTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             // matches pattern but invalid schema for object
@@ -87,7 +87,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/PatternTest.php b/tests/Constraints/PatternTest.php
index 3ffd2656..8207c91b 100644
--- a/tests/Constraints/PatternTest.php
+++ b/tests/Constraints/PatternTest.php
@@ -13,7 +13,7 @@ class PatternTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -51,7 +51,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/PointerTest.php b/tests/Constraints/PointerTest.php
index 09bcb755..1623f41b 100644
--- a/tests/Constraints/PointerTest.php
+++ b/tests/Constraints/PointerTest.php
@@ -16,7 +16,7 @@ class PointerTest extends TestCase
 {
     protected $validateSchema = true;
 
-    public function testVariousPointers()
+    public function testVariousPointers(): void
     {
         $schema = [
             'type' => 'object',
diff --git a/tests/Constraints/ReadOnlyTest.php b/tests/Constraints/ReadOnlyTest.php
index 95b98333..3a54fa51 100644
--- a/tests/Constraints/ReadOnlyTest.php
+++ b/tests/Constraints/ReadOnlyTest.php
@@ -13,7 +13,7 @@ class ReadOnlyTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         //is readonly really required?
         return [
@@ -29,7 +29,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/RequireTest.php b/tests/Constraints/RequireTest.php
index e90489d0..34ca88ca 100644
--- a/tests/Constraints/RequireTest.php
+++ b/tests/Constraints/RequireTest.php
@@ -13,7 +13,7 @@ class RequireTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -31,7 +31,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/RequiredPropertyTest.php b/tests/Constraints/RequiredPropertyTest.php
index d798ceff..2f38c3e5 100644
--- a/tests/Constraints/RequiredPropertyTest.php
+++ b/tests/Constraints/RequiredPropertyTest.php
@@ -20,7 +20,7 @@ class RequiredPropertyTest extends BaseTestCase
     protected $schemaSpec = 'http://json-schema.org/draft-03/schema#';
     protected $validateSchema = false;
 
-    public function testErrorPropertyIsPopulatedForRequiredIfMissingInInput()
+    public function testErrorPropertyIsPopulatedForRequiredIfMissingInInput(): void
     {
         $validator = new UndefinedConstraint();
         $document = json_decode(
@@ -44,7 +44,7 @@ public function testErrorPropertyIsPopulatedForRequiredIfMissingInInput()
         $this->assertErrorHasExpectedPropertyValue($error, 'foo');
     }
 
-    public function testPathErrorPropertyIsPopulatedForRequiredIfMissingInInput()
+    public function testPathErrorPropertyIsPopulatedForRequiredIfMissingInInput(): void
     {
         $validator = new UndefinedConstraint();
         $document = json_decode(
@@ -77,7 +77,7 @@ public function testPathErrorPropertyIsPopulatedForRequiredIfMissingInInput()
         $this->assertErrorHasExpectedPropertyValue($error, 'foo[0].bar');
     }
 
-    public function testErrorPropertyIsPopulatedForRequiredIfEmptyValueInInput()
+    public function testErrorPropertyIsPopulatedForRequiredIfEmptyValueInInput(): void
     {
         $validator = new UndefinedConstraint();
         $document = json_decode(
@@ -102,7 +102,7 @@ public function testErrorPropertyIsPopulatedForRequiredIfEmptyValueInInput()
         $this->assertErrorHasExpectedPropertyValue($error, 'foo');
     }
 
-    protected function assertErrorHasExpectedPropertyValue($error, $propertyValue)
+    protected function assertErrorHasExpectedPropertyValue($error, $propertyValue): void
     {
         if (!(isset($error[0]) && is_array($error[0]) && isset($error[0]['property']))) {
             $this->fail(
@@ -113,7 +113,7 @@ protected function assertErrorHasExpectedPropertyValue($error, $propertyValue)
         $this->assertEquals($propertyValue, $error[0]['property']);
     }
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -284,7 +284,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/SchemaValidationTest.php b/tests/Constraints/SchemaValidationTest.php
index f158cfe3..65268f49 100644
--- a/tests/Constraints/SchemaValidationTest.php
+++ b/tests/Constraints/SchemaValidationTest.php
@@ -17,7 +17,7 @@ class SchemaValidationTest extends TestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [// invalid v4 schema (uses v3 require)
@@ -44,7 +44,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [// valid v4 schema (uses v4 require)
@@ -64,7 +64,7 @@ public function getValidTests()
     /**
      * @dataProvider getInvalidTests
      */
-    public function testInvalidCases($schema)
+    public function testInvalidCases($schema): void
     {
         $input = json_decode('{"propertyOne":"valueOne"}');
         $schema = json_decode($schema);
@@ -85,7 +85,7 @@ public function testInvalidCases($schema)
     /**
      * @dataProvider getValidTests
      */
-    public function testValidCases($schema)
+    public function testValidCases($schema): void
     {
         $input = json_decode('{"propertyOne":"valueOne"}');
         $schema = json_decode($schema);
@@ -100,7 +100,7 @@ public function testValidCases($schema)
         $this->assertTrue($v->isValid(), 'Validation failed on a valid test case');
     }
 
-    public function testNonObjectSchema()
+    public function testNonObjectSchema(): void
     {
         $this->expectException('\JsonSchema\Exception\RuntimeException');
         $this->expectExceptionMessage('Cannot validate the schema of a non-object');
@@ -108,7 +108,7 @@ public function testNonObjectSchema()
         $this->testValidCases('"notAnObject"');
     }
 
-    public function testInvalidSchemaException()
+    public function testInvalidSchemaException(): void
     {
         $this->expectException('\JsonSchema\Exception\InvalidSchemaException');
         $this->expectExceptionMessage('Schema did not pass validation');
diff --git a/tests/Constraints/SelfDefinedSchemaTest.php b/tests/Constraints/SelfDefinedSchemaTest.php
index 2fcd4906..4ac1b8a7 100644
--- a/tests/Constraints/SelfDefinedSchemaTest.php
+++ b/tests/Constraints/SelfDefinedSchemaTest.php
@@ -15,7 +15,7 @@ class SelfDefinedSchemaTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -41,7 +41,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
@@ -67,7 +67,7 @@ public function getValidTests()
         ];
     }
 
-    public function testInvalidArgumentException()
+    public function testInvalidArgumentException(): void
     {
         $value = json_decode('{}');
         $schema = json_decode('');
diff --git a/tests/Constraints/TupleTypingTest.php b/tests/Constraints/TupleTypingTest.php
index 52feceb2..f565ae00 100644
--- a/tests/Constraints/TupleTypingTest.php
+++ b/tests/Constraints/TupleTypingTest.php
@@ -13,7 +13,7 @@ class TupleTypingTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -85,7 +85,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/TypeTest.php b/tests/Constraints/TypeTest.php
index 4b30dacb..1590d473 100644
--- a/tests/Constraints/TypeTest.php
+++ b/tests/Constraints/TypeTest.php
@@ -24,10 +24,8 @@ class TypeTest extends TestCase
 {
     /**
      * @see testIndefiniteArticleForTypeInTypeCheckErrorMessage
-     *
-     * @return array
      */
-    public function provideIndefiniteArticlesForTypes()
+    public function provideIndefiniteArticlesForTypes(): array
     {
         return [
             ['integer', 'an integer'],
@@ -46,7 +44,7 @@ public function provideIndefiniteArticlesForTypes()
     /**
      * @dataProvider provideIndefiniteArticlesForTypes
      */
-    public function testIndefiniteArticleForTypeInTypeCheckErrorMessage($type, $wording, $value = null, $label = 'NULL')
+    public function testIndefiniteArticleForTypeInTypeCheckErrorMessage($type, $wording, $value = null, $label = 'NULL'): void
     {
         $constraint = new TypeConstraint();
         $constraint->check($value, (object) ['type' => $type]);
@@ -56,7 +54,7 @@ public function testIndefiniteArticleForTypeInTypeCheckErrorMessage($type, $word
     /**
      * Test uncovered areas of the loose type checker
      */
-    public function testLooseTypeChecking()
+    public function testLooseTypeChecking(): void
     {
         $v = new \stdClass();
         $v->property = 'dataOne';
@@ -72,7 +70,7 @@ public function testLooseTypeChecking()
      * @param string         $expected
      * @param TypeConstraint $actual
      */
-    private function assertTypeConstraintError($expected, TypeConstraint $actual)
+    private function assertTypeConstraintError($expected, TypeConstraint $actual): void
     {
         $actualErrors = $actual->getErrors();
 
@@ -94,7 +92,7 @@ private function assertTypeConstraintError($expected, TypeConstraint $actual)
         $this->assertSame($expected, $actualMessage); // the same for the strictness
     }
 
-    public function validNameWordingDataProvider()
+    public function validNameWordingDataProvider(): array
     {
         $wordings = [];
 
@@ -108,7 +106,7 @@ public function validNameWordingDataProvider()
     /**
      * @dataProvider validNameWordingDataProvider
      */
-    public function testValidateTypeNameWording($nameWording)
+    public function testValidateTypeNameWording($nameWording): void
     {
         $t = new TypeConstraint();
         $r = new \ReflectionObject($t);
@@ -119,7 +117,7 @@ public function testValidateTypeNameWording($nameWording)
         $this->expectNotToPerformAssertions();
     }
 
-    public function testInvalidateTypeNameWording()
+    public function testInvalidateTypeNameWording(): void
     {
         $t = new TypeConstraint();
         $r = new \ReflectionObject($t);
@@ -132,7 +130,7 @@ public function testInvalidateTypeNameWording()
         $m->invoke($t, 'notAValidTypeName');
     }
 
-    public function testValidateTypeException()
+    public function testValidateTypeException(): void
     {
         $t = new TypeConstraint();
         $data = new \stdClass();
diff --git a/tests/Constraints/UnionTypesTest.php b/tests/Constraints/UnionTypesTest.php
index 9757b3c2..387848df 100644
--- a/tests/Constraints/UnionTypesTest.php
+++ b/tests/Constraints/UnionTypesTest.php
@@ -13,7 +13,7 @@ class UnionTypesTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -32,7 +32,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/UnionWithNullValueTest.php b/tests/Constraints/UnionWithNullValueTest.php
index ad5ea31e..16d2d8b2 100644
--- a/tests/Constraints/UnionWithNullValueTest.php
+++ b/tests/Constraints/UnionWithNullValueTest.php
@@ -13,7 +13,7 @@ class UnionWithNullValueTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -32,7 +32,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/UniqueItemsTest.php b/tests/Constraints/UniqueItemsTest.php
index 91843f45..7a2444ca 100644
--- a/tests/Constraints/UniqueItemsTest.php
+++ b/tests/Constraints/UniqueItemsTest.php
@@ -13,7 +13,7 @@ class UniqueItemsTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -61,7 +61,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Constraints/ValidationExceptionTest.php b/tests/Constraints/ValidationExceptionTest.php
index 317fc13f..ac6d973d 100644
--- a/tests/Constraints/ValidationExceptionTest.php
+++ b/tests/Constraints/ValidationExceptionTest.php
@@ -16,7 +16,7 @@
 
 class ValidationExceptionTest extends TestCase
 {
-    public function testValidationException()
+    public function testValidationException(): void
     {
         $exception = new ValidationException();
         $this->assertInstanceOf('\JsonSchema\Exception\ValidationException', $exception);
diff --git a/tests/Constraints/VeryBaseTestCase.php b/tests/Constraints/VeryBaseTestCase.php
index f12cba88..a19749a4 100644
--- a/tests/Constraints/VeryBaseTestCase.php
+++ b/tests/Constraints/VeryBaseTestCase.php
@@ -25,10 +25,8 @@ abstract class VeryBaseTestCase extends TestCase
 
     /**
      * @param object $schema
-     *
-     * @return object
      */
-    protected function getUriRetrieverMock($schema)
+    protected function getUriRetrieverMock($schema): object
     {
         $relativeTestsRoot = realpath(__DIR__ . '/../../vendor/json-schema/json-schema-test-suite/remotes');
 
@@ -60,10 +58,7 @@ protected function getUriRetrieverMock($schema)
         return $uriRetriever->reveal();
     }
 
-    /**
-     * @return object
-     */
-    private function getJsonSchemaDraft03()
+    private function getJsonSchemaDraft03(): object
     {
         if (!$this->jsonSchemaDraft03) {
             $this->jsonSchemaDraft03 = json_decode(
@@ -74,10 +69,7 @@ private function getJsonSchemaDraft03()
         return $this->jsonSchemaDraft03;
     }
 
-    /**
-     * @return object
-     */
-    private function getJsonSchemaDraft04()
+    private function getJsonSchemaDraft04(): object
     {
         if (!$this->jsonSchemaDraft04) {
             $this->jsonSchemaDraft04 = json_decode(
diff --git a/tests/Constraints/WrongMessagesFailingTestCaseTest.php b/tests/Constraints/WrongMessagesFailingTestCaseTest.php
index aae9b552..e36f57ce 100644
--- a/tests/Constraints/WrongMessagesFailingTestCaseTest.php
+++ b/tests/Constraints/WrongMessagesFailingTestCaseTest.php
@@ -13,7 +13,7 @@ class WrongMessagesFailingTestCaseTest extends BaseTestCase
 {
     protected $validateSchema = true;
 
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return [
             [
@@ -32,7 +32,7 @@ public function getInvalidTests()
         ];
     }
 
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return [
             [
diff --git a/tests/Drafts/BaseDraftTestCase.php b/tests/Drafts/BaseDraftTestCase.php
index cd2d4c86..42cfd988 100644
--- a/tests/Drafts/BaseDraftTestCase.php
+++ b/tests/Drafts/BaseDraftTestCase.php
@@ -12,7 +12,7 @@ abstract class BaseDraftTestCase extends BaseTestCase
     /** @var string */
     protected $relativeTestsRoot = '/../../vendor/json-schema/json-schema-test-suite/tests';
 
-    private function setUpTests($isValid)
+    private function setUpTests($isValid): array
     {
         $filePaths = $this->getFilePaths();
         $skippedTests = $this->getSkippedTests();
@@ -46,7 +46,7 @@ private function setUpTests($isValid)
     /**
      * {@inheritdoc}
      */
-    public function getInvalidTests()
+    public function getInvalidTests(): array
     {
         return $this->setUpTests(false);
     }
@@ -54,7 +54,7 @@ public function getInvalidTests()
     /**
      * {@inheritdoc}
      */
-    public function getValidTests()
+    public function getValidTests(): array
     {
         return $this->setUpTests(true);
     }
@@ -62,12 +62,12 @@ public function getValidTests()
     /**
      * @return string[]
      */
-    abstract protected function getFilePaths();
+    abstract protected function getFilePaths(): array;
 
     /**
      * @return string[]
      */
-    abstract protected function getSkippedTests();
+    abstract protected function getSkippedTests(): array;
 
     /**
      * Generates a readable path to Json Schema Test Suite data set under test
@@ -75,10 +75,8 @@ abstract protected function getSkippedTests();
      * @param string $filename
      * @param string $suiteDesc
      * @param string $testCaseDesc
-     *
-     * @return string
      */
-    private function createDataSetPath($filename, $suiteDesc, $testCaseDesc)
+    private function createDataSetPath($filename, $suiteDesc, $testCaseDesc): string
     {
         $separator = ' / ';
 
diff --git a/tests/Drafts/Draft3Test.php b/tests/Drafts/Draft3Test.php
index f6cf41ad..42982062 100644
--- a/tests/Drafts/Draft3Test.php
+++ b/tests/Drafts/Draft3Test.php
@@ -20,7 +20,7 @@ class Draft3Test extends BaseDraftTestCase
     /**
      * {@inheritdoc}
      */
-    protected function getFilePaths()
+    protected function getFilePaths(): array
     {
         return [
             realpath(__DIR__ . $this->relativeTestsRoot . '/draft3'),
@@ -28,7 +28,7 @@ protected function getFilePaths()
         ];
     }
 
-    public function getInvalidForAssocTests()
+    public function getInvalidForAssocTests(): array
     {
         $tests = parent::getInvalidForAssocTests();
         unset(
@@ -39,7 +39,7 @@ public function getInvalidForAssocTests()
         return $tests;
     }
 
-    public function getValidForAssocTests()
+    public function getValidForAssocTests(): array
     {
         $tests = parent::getValidForAssocTests();
         unset(
@@ -53,7 +53,7 @@ public function getValidForAssocTests()
     /**
      * {@inheritdoc}
      */
-    protected function getSkippedTests()
+    protected function getSkippedTests(): array
     {
         return [
             // Optional
diff --git a/tests/Drafts/Draft4Test.php b/tests/Drafts/Draft4Test.php
index e129ad80..e2b8a602 100644
--- a/tests/Drafts/Draft4Test.php
+++ b/tests/Drafts/Draft4Test.php
@@ -20,7 +20,7 @@ class Draft4Test extends BaseDraftTestCase
     /**
      * {@inheritdoc}
      */
-    protected function getFilePaths()
+    protected function getFilePaths(): array
     {
         return [
             realpath(__DIR__ . $this->relativeTestsRoot . '/draft4'),
@@ -28,7 +28,7 @@ protected function getFilePaths()
         ];
     }
 
-    public function getInvalidForAssocTests()
+    public function getInvalidForAssocTests(): array
     {
         $tests = parent::getInvalidForAssocTests();
         unset(
@@ -39,7 +39,7 @@ public function getInvalidForAssocTests()
         return $tests;
     }
 
-    public function getValidForAssocTests()
+    public function getValidForAssocTests(): array
     {
         $tests = parent::getValidForAssocTests();
         unset(
@@ -53,7 +53,7 @@ public function getValidForAssocTests()
     /**
      * {@inheritdoc}
      */
-    protected function getSkippedTests()
+    protected function getSkippedTests(): array
     {
         return [
             // Optional
diff --git a/tests/Entity/JsonPointerTest.php b/tests/Entity/JsonPointerTest.php
index 48203824..f8477b5d 100644
--- a/tests/Entity/JsonPointerTest.php
+++ b/tests/Entity/JsonPointerTest.php
@@ -34,7 +34,7 @@ public function testJsonPointer(
         $expectedPropertyPaths,
         $expectedPropertyPathAsString,
         $expectedToString
-    ) {
+    ): void {
         $jsonPointer = new JsonPointer($testValue);
         $this->assertEquals($expectedFileName, $jsonPointer->getFilename());
         $this->assertEquals($expectedPropertyPaths, $jsonPointer->getPropertyPaths());
@@ -42,10 +42,7 @@ public function testJsonPointer(
         $this->assertEquals($expectedToString, (string) $jsonPointer);
     }
 
-    /**
-     * @return array[]
-     */
-    public function getTestData()
+    public function getTestData(): array
     {
         return [
             'testDataSet_01' => [
@@ -93,7 +90,7 @@ public function getTestData()
         ];
     }
 
-    public function testJsonPointerWithPropertyPaths()
+    public function testJsonPointerWithPropertyPaths(): void
     {
         $initial = new JsonPointer('#/definitions/date');
 
@@ -111,7 +108,7 @@ public function testJsonPointerWithPropertyPaths()
         $this->assertEquals('#/~0definitions~1general/%25custom%25', $modified->getPropertyPathAsString());
     }
 
-    public function testCreateWithInvalidValue()
+    public function testCreateWithInvalidValue(): void
     {
         $this->expectException('\JsonSchema\Exception\InvalidArgumentException');
         $this->expectExceptionMessage('Ref value must be a string');
diff --git a/tests/Exception/InvalidArgumentExceptionTest.php b/tests/Exception/InvalidArgumentExceptionTest.php
index 5715fbac..01243760 100644
--- a/tests/Exception/InvalidArgumentExceptionTest.php
+++ b/tests/Exception/InvalidArgumentExceptionTest.php
@@ -7,7 +7,7 @@
 
 class InvalidArgumentExceptionTest extends TestCase
 {
-    public function testHierarchy()
+    public function testHierarchy(): void
     {
         $exception = new InvalidArgumentException();
         self::assertInstanceOf('\InvalidArgumentException', $exception);
diff --git a/tests/Exception/InvalidSchemaMediaTypeExceptionTest.php b/tests/Exception/InvalidSchemaMediaTypeExceptionTest.php
index 6b12adc6..c3930db9 100644
--- a/tests/Exception/InvalidSchemaMediaTypeExceptionTest.php
+++ b/tests/Exception/InvalidSchemaMediaTypeExceptionTest.php
@@ -7,7 +7,7 @@
 
 class InvalidSchemaMediaTypeExceptionTest extends TestCase
 {
-    public function testHierarchy()
+    public function testHierarchy(): void
     {
         $exception = new InvalidSchemaMediaTypeException();
         self::assertInstanceOf('\RuntimeException', $exception);
diff --git a/tests/Exception/InvalidSourceUriExceptionTest.php b/tests/Exception/InvalidSourceUriExceptionTest.php
index 7cccf817..c7fd48bc 100644
--- a/tests/Exception/InvalidSourceUriExceptionTest.php
+++ b/tests/Exception/InvalidSourceUriExceptionTest.php
@@ -7,7 +7,7 @@
 
 class InvalidSourceUriExceptionTest extends TestCase
 {
-    public function testHierarchy()
+    public function testHierarchy(): void
     {
         $exception = new InvalidSourceUriException();
         self::assertInstanceOf('\InvalidArgumentException', $exception);
diff --git a/tests/Exception/JsonDecodingExceptionTest.php b/tests/Exception/JsonDecodingExceptionTest.php
index 667c6520..468165e4 100644
--- a/tests/Exception/JsonDecodingExceptionTest.php
+++ b/tests/Exception/JsonDecodingExceptionTest.php
@@ -7,7 +7,7 @@
 
 class JsonDecodingExceptionTest extends TestCase
 {
-    public function testHierarchy()
+    public function testHierarchy(): void
     {
         $exception = new JsonDecodingException();
         self::assertInstanceOf('\RuntimeException', $exception);
diff --git a/tests/Exception/ResourceNotFoundExceptionTest.php b/tests/Exception/ResourceNotFoundExceptionTest.php
index 2cde0eec..fe87575c 100644
--- a/tests/Exception/ResourceNotFoundExceptionTest.php
+++ b/tests/Exception/ResourceNotFoundExceptionTest.php
@@ -7,7 +7,7 @@
 
 class ResourceNotFoundExceptionTest extends TestCase
 {
-    public function testHierarchy()
+    public function testHierarchy(): void
     {
         $exception = new ResourceNotFoundException();
         self::assertInstanceOf('\RuntimeException', $exception);
diff --git a/tests/Exception/RuntimeExceptionTest.php b/tests/Exception/RuntimeExceptionTest.php
index 4db22eaa..cf34439b 100644
--- a/tests/Exception/RuntimeExceptionTest.php
+++ b/tests/Exception/RuntimeExceptionTest.php
@@ -7,7 +7,7 @@
 
 class RuntimeExceptionTest extends TestCase
 {
-    public function testHierarchy()
+    public function testHierarchy(): void
     {
         $exception = new RuntimeException();
         self::assertInstanceOf('\RuntimeException', $exception);
diff --git a/tests/Exception/UnresolvableJsonPointerExceptionTest.php b/tests/Exception/UnresolvableJsonPointerExceptionTest.php
index f061d9da..5255c5c5 100644
--- a/tests/Exception/UnresolvableJsonPointerExceptionTest.php
+++ b/tests/Exception/UnresolvableJsonPointerExceptionTest.php
@@ -7,7 +7,7 @@
 
 class UnresolvableJsonPointerExceptionTest extends TestCase
 {
-    public function testHierarchy()
+    public function testHierarchy(): void
     {
         $exception = new UnresolvableJsonPointerException();
         self::assertInstanceOf('\InvalidArgumentException', $exception);
diff --git a/tests/Exception/UriResolverExceptionTest.php b/tests/Exception/UriResolverExceptionTest.php
index eb9af83f..630f30a2 100644
--- a/tests/Exception/UriResolverExceptionTest.php
+++ b/tests/Exception/UriResolverExceptionTest.php
@@ -7,7 +7,7 @@
 
 class UriResolverExceptionTest extends TestCase
 {
-    public function testHierarchy()
+    public function testHierarchy(): void
     {
         $exception = new UriResolverException();
         self::assertInstanceOf('\RuntimeException', $exception);
diff --git a/tests/Iterators/ObjectIteratorTest.php b/tests/Iterators/ObjectIteratorTest.php
index 80b711f3..258a0156 100644
--- a/tests/Iterators/ObjectIteratorTest.php
+++ b/tests/Iterators/ObjectIteratorTest.php
@@ -35,28 +35,28 @@ public function setUp(): void
         ];
     }
 
-    public function testCreate()
+    public function testCreate(): void
     {
         $i = new ObjectIterator($this->testObject);
 
         $this->assertInstanceOf('\JsonSchema\Iterator\ObjectIterator', $i);
     }
 
-    public function testInitialState()
+    public function testInitialState(): void
     {
         $i = new ObjectIterator($this->testObject);
 
         $this->assertEquals($this->testObject, $i->current());
     }
 
-    public function testCount()
+    public function testCount(): void
     {
         $i = new ObjectIterator($this->testObject);
 
         $this->assertEquals(4, $i->count());
     }
 
-    public function testKey()
+    public function testKey(): void
     {
         $i = new ObjectIterator($this->testObject);
 
@@ -67,7 +67,7 @@ public function testKey()
         $this->assertEquals($this->testObject->subTwo->subThree, $i->current());
     }
 
-    public function testAlwaysObjects()
+    public function testAlwaysObjects(): void
     {
         $i= new ObjectIterator($this->testObject);
 
@@ -76,7 +76,7 @@ public function testAlwaysObjects()
         }
     }
 
-    public function testReachesAllProperties()
+    public function testReachesAllProperties(): void
     {
         $i = new ObjectIterator($this->testObject);
 
diff --git a/tests/RefTest.php b/tests/RefTest.php
index 94f9cf91..3b66d586 100644
--- a/tests/RefTest.php
+++ b/tests/RefTest.php
@@ -14,7 +14,7 @@
 
 class RefTest extends TestCase
 {
-    public function dataRefIgnoresSiblings()
+    public function dataRefIgnoresSiblings(): array
     {
         return [
             // #0 check that $ref is resolved and the instance is validated against
@@ -62,7 +62,7 @@ public function dataRefIgnoresSiblings()
     }
 
     /** @dataProvider dataRefIgnoresSiblings */
-    public function testRefIgnoresSiblings($schema, $document, $isValid, $exception = null)
+    public function testRefIgnoresSiblings($schema, $document, $isValid, $exception = null): void
     {
         $document = json_decode($document);
         $schema = json_decode($schema);
diff --git a/tests/Rfc3339Test.php b/tests/Rfc3339Test.php
index 890aa57e..73c1d597 100644
--- a/tests/Rfc3339Test.php
+++ b/tests/Rfc3339Test.php
@@ -12,7 +12,7 @@ class Rfc3339Test extends TestCase
      * @param \DateTime|null $expected
      * @dataProvider provideValidFormats
      */
-    public function testCreateFromValidString($string, \DateTime $expected)
+    public function testCreateFromValidString($string, \DateTime $expected): void
     {
         $actual = Rfc3339::createFromString($string);
 
@@ -24,12 +24,12 @@ public function testCreateFromValidString($string, \DateTime $expected)
      * @param string $string
      * @dataProvider provideInvalidFormats
      */
-    public function testCreateFromInvalidString($string)
+    public function testCreateFromInvalidString($string): void
     {
         $this->assertNull(Rfc3339::createFromString($string), sprintf('String "%s" should not be converted to DateTime', $string));
     }
 
-    public function provideValidFormats()
+    public function provideValidFormats(): array
     {
         return [
             [
@@ -63,7 +63,7 @@ public function provideValidFormats()
         ];
     }
 
-    public function provideInvalidFormats()
+    public function provideInvalidFormats(): array
     {
         return [
             ['1999-1-11T00:00:00Z'],
diff --git a/tests/SchemaStorageTest.php b/tests/SchemaStorageTest.php
index 8dd7e582..812fe804 100644
--- a/tests/SchemaStorageTest.php
+++ b/tests/SchemaStorageTest.php
@@ -16,7 +16,7 @@
 
 class SchemaStorageTest extends TestCase
 {
-    public function testResolveRef()
+    public function testResolveRef(): void
     {
         $mainSchema = $this->getMainSchema();
         $mainSchemaPath = 'http://www.example.com/schema.json';
@@ -32,7 +32,7 @@ public function testResolveRef()
         );
     }
 
-    public function testResolveTopRef()
+    public function testResolveTopRef(): void
     {
         $input = json_decode('{"propertyOne":"notANumber"}');
         $schema = json_decode('{"$ref":"#/definition","definition":{"properties":{"propertyOne":{"type":"number"}}}}');
@@ -44,7 +44,7 @@ public function testResolveTopRef()
     /**
      * @depends testResolveRef
      */
-    public function testSchemaWithLocalAndExternalReferencesWithCircularReference()
+    public function testSchemaWithLocalAndExternalReferencesWithCircularReference(): void
     {
         $mainSchema = $this->getMainSchema();
         $schema2 = $this->getSchema2();
@@ -100,7 +100,7 @@ public function testSchemaWithLocalAndExternalReferencesWithCircularReference()
         );
     }
 
-    public function testUnresolvableJsonPointExceptionShouldBeThrown()
+    public function testUnresolvableJsonPointExceptionShouldBeThrown(): void
     {
         $this->expectException('JsonSchema\Exception\UnresolvableJsonPointerException');
         $this->expectExceptionMessage('File: http://www.example.com/schema.json is found, but could not resolve fragment: #/definitions/car');
@@ -117,7 +117,7 @@ public function testUnresolvableJsonPointExceptionShouldBeThrown()
         $schemaStorage->resolveRef("$mainSchemaPath#/definitions/car");
     }
 
-    public function testResolveRefWithNoAssociatedFileName()
+    public function testResolveRefWithNoAssociatedFileName(): void
     {
         $this->expectException('JsonSchema\Exception\UnresolvableJsonPointerException');
         $this->expectExceptionMessage("Could not resolve fragment '#': no file is defined");
@@ -126,10 +126,7 @@ public function testResolveRefWithNoAssociatedFileName()
         $schemaStorage->resolveRef('#');
     }
 
-    /**
-     * @return object
-     */
-    private function getMainSchema()
+    private function getMainSchema(): object
     {
         return (object) [
             'version' => 'v1',
@@ -188,10 +185,7 @@ private function getMainSchema()
         ];
     }
 
-    /**
-     * @return object
-     */
-    private function getSchema2()
+    private function getSchema2(): object
     {
         return (object) [
             'version' => 'v1',
@@ -218,10 +212,7 @@ private function getSchema2()
         ];
     }
 
-    /**
-     * @return object
-     */
-    private function getSchema3()
+    private function getSchema3(): object
     {
         return (object) [
             'version' => 'v1',
@@ -243,10 +234,7 @@ private function getSchema3()
         ];
     }
 
-    /**
-     * @return object
-     */
-    private function getInvalidSchema()
+    private function getInvalidSchema(): object
     {
         return (object) [
             'version' => 'v1',
@@ -272,21 +260,21 @@ private function getInvalidSchema()
         ];
     }
 
-    public function testGetUriRetriever()
+    public function testGetUriRetriever(): void
     {
         $s = new SchemaStorage();
         $s->addSchema('http://json-schema.org/draft-04/schema#');
         $this->assertInstanceOf('\JsonSchema\Uri\UriRetriever', $s->getUriRetriever());
     }
 
-    public function testGetUriResolver()
+    public function testGetUriResolver(): void
     {
         $s = new SchemaStorage();
         $s->addSchema('http://json-schema.org/draft-04/schema#');
         $this->assertInstanceOf('\JsonSchema\Uri\UriResolver', $s->getUriResolver());
     }
 
-    public function testMetaSchemaFixes()
+    public function testMetaSchemaFixes(): void
     {
         $s = new SchemaStorage();
         $s->addSchema('http://json-schema.org/draft-03/schema#');
@@ -299,7 +287,7 @@ public function testMetaSchemaFixes()
         $this->assertEquals('uri-reference', $draft_04->properties->id->format);
     }
 
-    public function testNoDoubleResolve()
+    public function testNoDoubleResolve(): void
     {
         $schemaOne = json_decode('{"id": "test/schema", "$ref": "../test2/schema2"}');
 
diff --git a/tests/Uri/Retrievers/CurlTest.php b/tests/Uri/Retrievers/CurlTest.php
index bac8c32e..5715773d 100644
--- a/tests/Uri/Retrievers/CurlTest.php
+++ b/tests/Uri/Retrievers/CurlTest.php
@@ -7,7 +7,7 @@
 
     class CurlTest extends TestCase
     {
-        public function testRetrieveFile()
+        public function testRetrieveFile(): void
         {
             $c = new Curl();
             $result = $c->retrieve(realpath(__DIR__ . '/../../fixtures/foobar.json'));
@@ -15,7 +15,7 @@ public function testRetrieveFile()
             self::assertStringEqualsFileCanonicalizing(realpath(__DIR__ . '/../../fixtures/foobar.json'), $result);
         }
 
-        public function testRetrieveNonexistantFile()
+        public function testRetrieveNonexistantFile(): void
         {
             $c = new Curl();
 
@@ -25,7 +25,7 @@ public function testRetrieveNonexistantFile()
             $c->retrieve(__DIR__ . '/notARealFile');
         }
 
-        public function testNoContentType()
+        public function testNoContentType(): void
         {
             $c = new Curl();
             $result = $c->retrieve(realpath(__DIR__ . '/../../fixtures') . '/foobar-noheader.json');
diff --git a/tests/Uri/Retrievers/FileGetContentsTest.php b/tests/Uri/Retrievers/FileGetContentsTest.php
index eab18b2f..57e6c90a 100644
--- a/tests/Uri/Retrievers/FileGetContentsTest.php
+++ b/tests/Uri/Retrievers/FileGetContentsTest.php
@@ -10,7 +10,7 @@
  */
 class FileGetContentsTest extends TestCase
 {
-    public function testFetchMissingFile()
+    public function testFetchMissingFile(): void
     {
         $res = new FileGetContents();
 
@@ -19,14 +19,14 @@ public function testFetchMissingFile()
         $res->retrieve(__DIR__ . '/Fixture/missing.json');
     }
 
-    public function testFetchFile()
+    public function testFetchFile(): void
     {
         $res = new FileGetContents();
         $result = $res->retrieve(__DIR__ . '/../Fixture/child.json');
         $this->assertNotEmpty($result);
     }
 
-    public function testContentType()
+    public function testContentType(): void
     {
         $res = new FileGetContents();
 
@@ -38,7 +38,7 @@ public function testContentType()
         $this->assertFalse($fetchContentType->invoke($res, ['X-Some-Header: whateverValue']));
     }
 
-    public function testCanHandleHttp301PermanentRedirect()
+    public function testCanHandleHttp301PermanentRedirect(): void
     {
         $res = new FileGetContents();
 
diff --git a/tests/Uri/Retrievers/PredefinedArrayTest.php b/tests/Uri/Retrievers/PredefinedArrayTest.php
index 7572a88b..c5436506 100644
--- a/tests/Uri/Retrievers/PredefinedArrayTest.php
+++ b/tests/Uri/Retrievers/PredefinedArrayTest.php
@@ -23,19 +23,19 @@ public function setUp(): void
         );
     }
 
-    public function testRetrieve()
+    public function testRetrieve(): void
     {
         $this->assertEquals('THE_PERSON_SCHEMA', $this->retriever->retrieve('http://acme.com/schemas/person#'));
         $this->assertEquals('THE_ADDRESS_SCHEMA', $this->retriever->retrieve('http://acme.com/schemas/address#'));
     }
 
-    public function testRetrieveNonExistsingSchema()
+    public function testRetrieveNonExistsingSchema(): void
     {
         $this->expectException(\JsonSchema\Exception\ResourceNotFoundException::class);
         $this->retriever->retrieve('http://acme.com/schemas/plop#');
     }
 
-    public function testGetContentType()
+    public function testGetContentType(): void
     {
         $this->assertEquals('THE_CONTENT_TYPE', $this->retriever->getContentType());
     }
diff --git a/tests/Uri/UriResolverTest.php b/tests/Uri/UriResolverTest.php
index 98b48a2e..898f360f 100644
--- a/tests/Uri/UriResolverTest.php
+++ b/tests/Uri/UriResolverTest.php
@@ -14,7 +14,7 @@ public function setUp(): void
         $this->resolver = new UriResolver();
     }
 
-    public function testParse()
+    public function testParse(): void
     {
         $this->assertEquals(
             [
@@ -26,7 +26,7 @@ public function testParse()
         );
     }
 
-    public function testParseAnchor()
+    public function testParseAnchor(): void
     {
         $this->assertEquals(
             [
@@ -40,7 +40,7 @@ public function testParseAnchor()
         );
     }
 
-    public function testCombineRelativePathWithBasePath()
+    public function testCombineRelativePathWithBasePath(): void
     {
         $this->assertEquals(
             '/foo/baz.json',
@@ -51,7 +51,7 @@ public function testCombineRelativePathWithBasePath()
         );
     }
 
-    public function testCombineRelativePathWithBasePathAbsolute()
+    public function testCombineRelativePathWithBasePathAbsolute(): void
     {
         $this->assertEquals(
             '/baz/data.json',
@@ -62,7 +62,7 @@ public function testCombineRelativePathWithBasePathAbsolute()
         );
     }
 
-    public function testCombineRelativePathWithBasePathRelativeSub()
+    public function testCombineRelativePathWithBasePathRelativeSub(): void
     {
         $this->assertEquals(
             '/foo/baz/data.json',
@@ -73,7 +73,7 @@ public function testCombineRelativePathWithBasePathRelativeSub()
         );
     }
 
-    public function testCombineRelativePathWithBasePathNoPath()
+    public function testCombineRelativePathWithBasePathNoPath(): void
     {
         //needed for anchor-only urls
         $this->assertEquals(
@@ -85,7 +85,7 @@ public function testCombineRelativePathWithBasePathNoPath()
         );
     }
 
-    public function testResolveAbsoluteUri()
+    public function testResolveAbsoluteUri(): void
     {
         $this->assertEquals(
             'http://example.org/foo/bar.json',
@@ -96,13 +96,13 @@ public function testResolveAbsoluteUri()
         );
     }
 
-    public function testResolveRelativeUriNoBase()
+    public function testResolveRelativeUriNoBase(): void
     {
         $this->expectException(\JsonSchema\Exception\UriResolverException::class);
         $this->resolver->resolve('bar.json', null);
     }
 
-    public function testResolveRelativeUriBaseDir()
+    public function testResolveRelativeUriBaseDir(): void
     {
         $this->assertEquals(
             'http://example.org/foo/bar.json',
@@ -113,7 +113,7 @@ public function testResolveRelativeUriBaseDir()
         );
     }
 
-    public function testResolveRelativeUriBaseFile()
+    public function testResolveRelativeUriBaseFile(): void
     {
         $this->assertEquals(
             'http://example.org/foo/bar.json',
@@ -124,7 +124,7 @@ public function testResolveRelativeUriBaseFile()
         );
     }
 
-    public function testResolveAnchor()
+    public function testResolveAnchor(): void
     {
         $this->assertEquals(
             'http://example.org/foo/bar.json#baz',
@@ -135,7 +135,7 @@ public function testResolveAnchor()
         );
     }
 
-    public function testResolveAnchorWithFile()
+    public function testResolveAnchorWithFile(): void
     {
         $this->assertEquals(
             'http://example.org/foo/baz.json#baz',
@@ -146,7 +146,7 @@ public function testResolveAnchorWithFile()
         );
     }
 
-    public function testResolveAnchorAnchor()
+    public function testResolveAnchorAnchor(): void
     {
         $this->assertEquals(
             'http://example.org/foo/bar.json#bazinga',
@@ -157,7 +157,7 @@ public function testResolveAnchorAnchor()
         );
     }
 
-    public function testResolveEmpty()
+    public function testResolveEmpty(): void
     {
         $this->assertEquals(
             'http://example.org/foo/bar.json',
@@ -168,7 +168,7 @@ public function testResolveEmpty()
         );
     }
 
-    public function testReversable()
+    public function testReversable(): void
     {
         $uri = 'scheme://user:password@authority/path?query#fragment';
         $split = $this->resolver->parse($uri);
@@ -186,7 +186,7 @@ public function testReversable()
         $this->assertEquals($uri, $this->resolver->generate($split));
     }
 
-    public function testRelativeFileAsRoot()
+    public function testRelativeFileAsRoot(): void
     {
         $this->assertEquals(
             'file://' . getcwd() . '/src/JsonSchema/Validator.php',
@@ -197,7 +197,7 @@ public function testRelativeFileAsRoot()
         );
     }
 
-    public function testRelativeDirectoryAsRoot()
+    public function testRelativeDirectoryAsRoot(): void
     {
         $this->assertEquals(
             'file://' . getcwd() . '/src/JsonSchema/Validator.php',
@@ -208,7 +208,7 @@ public function testRelativeDirectoryAsRoot()
         );
     }
 
-    public function testRelativeNonExistentFileAsRoot()
+    public function testRelativeNonExistentFileAsRoot(): void
     {
         $this->assertEquals(
             'file://' . getcwd() . '/resolved.file',
diff --git a/tests/Uri/UriRetrieverTest.php b/tests/Uri/UriRetrieverTest.php
index 94e59bd9..81419269 100644
--- a/tests/Uri/UriRetrieverTest.php
+++ b/tests/Uri/UriRetrieverTest.php
@@ -50,7 +50,7 @@ private function getRetrieverMock($returnSchema)
     /**
      * @dataProvider jsonProvider
      */
-    public function testChildExtendsParentValidTest($childSchema, $parentSchema)
+    public function testChildExtendsParentValidTest($childSchema, $parentSchema): void
     {
         $this->mockRetriever($parentSchema);
 
@@ -65,7 +65,7 @@ public function testChildExtendsParentValidTest($childSchema, $parentSchema)
     /**
      * @dataProvider jsonProvider
      */
-    public function testChildExtendsParentInvalidChildTest($childSchema, $parentSchema)
+    public function testChildExtendsParentInvalidChildTest($childSchema, $parentSchema): void
     {
         $this->mockRetriever($parentSchema);
 
@@ -80,7 +80,7 @@ public function testChildExtendsParentInvalidChildTest($childSchema, $parentSche
     /**
      * @dataProvider jsonProvider
      */
-    public function testChildExtendsParentInvalidParentTest($childSchema, $parentSchema)
+    public function testChildExtendsParentInvalidParentTest($childSchema, $parentSchema): void
     {
         $this->mockRetriever($parentSchema);
 
@@ -95,7 +95,7 @@ public function testChildExtendsParentInvalidParentTest($childSchema, $parentSch
     /**
      * @dataProvider jsonProvider
      */
-    public function testResolveRelativeUri($childSchema, $parentSchema)
+    public function testResolveRelativeUri($childSchema, $parentSchema): void
     {
         self::setParentSchemaExtendsValue($parentSchema, 'grandparent');
         $this->mockRetriever($parentSchema);
@@ -108,14 +108,14 @@ public function testResolveRelativeUri($childSchema, $parentSchema)
         $this->assertTrue($this->validator->isValid());
     }
 
-    private static function setParentSchemaExtendsValue(&$parentSchema, $value)
+    private static function setParentSchemaExtendsValue(&$parentSchema, $value): void
     {
         $parentSchemaDecoded = json_decode($parentSchema, true);
         $parentSchemaDecoded['extends'] = $value;
         $parentSchema = json_encode($parentSchemaDecoded);
     }
 
-    public function jsonProvider()
+    public function jsonProvider(): array
     {
         $childSchema = <<<EOF
 {
@@ -150,7 +150,7 @@ public function jsonProvider()
         ];
     }
 
-    public function testResolvePointerNoFragment()
+    public function testResolvePointerNoFragment(): void
     {
         $schema = (object) [
             'title' => 'schema'
@@ -165,7 +165,7 @@ public function testResolvePointerNoFragment()
         );
     }
 
-    public function testResolvePointerFragment()
+    public function testResolvePointerFragment(): void
     {
         $schema = (object) [
             'definitions' => (object) [
@@ -185,7 +185,7 @@ public function testResolvePointerFragment()
         );
     }
 
-    public function testResolvePointerFragmentNotFound()
+    public function testResolvePointerFragmentNotFound(): void
     {
         $schema = (object) [
             'definitions' => (object) [
@@ -204,7 +204,7 @@ public function testResolvePointerFragmentNotFound()
         );
     }
 
-    public function testResolvePointerFragmentNoArray()
+    public function testResolvePointerFragmentNoArray(): void
     {
         $schema = (object) [
             'definitions' => (object) [
@@ -223,7 +223,7 @@ public function testResolvePointerFragmentNoArray()
         );
     }
 
-    public function testResolveExcessLevelUp()
+    public function testResolveExcessLevelUp(): void
     {
         $retriever = new UriRetriever();
 
@@ -233,7 +233,7 @@ public function testResolveExcessLevelUp()
         );
     }
 
-    public function testConfirmMediaTypeAcceptsJsonSchemaType()
+    public function testConfirmMediaTypeAcceptsJsonSchemaType(): void
     {
         $uriRetriever = $this->createMock('JsonSchema\Uri\Retrievers\UriRetrieverInterface');
         $retriever = new UriRetriever();
@@ -245,7 +245,7 @@ public function testConfirmMediaTypeAcceptsJsonSchemaType()
         $this->assertEquals(null, $retriever->confirmMediaType($uriRetriever, null));
     }
 
-    public function testConfirmMediaTypeAcceptsJsonType()
+    public function testConfirmMediaTypeAcceptsJsonType(): void
     {
         $uriRetriever = $this->createMock('JsonSchema\Uri\Retrievers\UriRetrieverInterface');
         $retriever = new UriRetriever();
@@ -257,7 +257,7 @@ public function testConfirmMediaTypeAcceptsJsonType()
         $this->assertEquals(null, $retriever->confirmMediaType($uriRetriever, null));
     }
 
-    public function testConfirmMediaTypeThrowsExceptionForUnsupportedTypes()
+    public function testConfirmMediaTypeThrowsExceptionForUnsupportedTypes(): void
     {
         $uriRetriever = $this->createMock('JsonSchema\Uri\Retrievers\UriRetrieverInterface');
         $retriever = new UriRetriever();
@@ -270,7 +270,7 @@ public function testConfirmMediaTypeThrowsExceptionForUnsupportedTypes()
         $retriever->confirmMediaType($uriRetriever, null);
     }
 
-    private function mockRetriever($schema)
+    private function mockRetriever($schema): void
     {
         $retrieverMock = $this->getRetrieverMock($schema);
 
@@ -283,7 +283,7 @@ private function mockRetriever($schema)
         $retriever->setValue($factory, $retrieverMock);
     }
 
-    public function testTranslations()
+    public function testTranslations(): void
     {
         $retriever = new UriRetriever();
 
@@ -294,7 +294,7 @@ public function testTranslations()
         $this->assertEquals($translated, $retriever->translate($uri));
     }
 
-    public function testPackageURITranslation()
+    public function testPackageURITranslation(): void
     {
         $retriever = new UriRetriever();
         $root = sprintf('file://%s/', realpath(__DIR__ . '/../..'));
@@ -303,7 +303,7 @@ public function testPackageURITranslation()
         $this->assertEquals("{$root}foo/bar.json", $uri);
     }
 
-    public function testDefaultDistTranslations()
+    public function testDefaultDistTranslations(): void
     {
         $retriever = new UriRetriever();
         $root = sprintf('file://%s/dist/schema/', realpath(__DIR__ . '/../..'));
@@ -319,7 +319,7 @@ public function testDefaultDistTranslations()
         );
     }
 
-    public function testRetrieveSchemaFromPackage()
+    public function testRetrieveSchemaFromPackage(): void
     {
         $retriever = new UriRetriever();
 
@@ -331,7 +331,7 @@ public function testRetrieveSchemaFromPackage()
         $this->assertEquals('454f423bd7edddf0bc77af4130ed9161', md5(json_encode($schema)));
     }
 
-    public function testInvalidContentTypeEndpointsDefault()
+    public function testInvalidContentTypeEndpointsDefault(): void
     {
         $mock = $this->createMock('JsonSchema\Uri\Retrievers\UriRetrieverInterface');
         $mock->method('getContentType')->willReturn('Application/X-Fake-Type');
@@ -341,7 +341,7 @@ public function testInvalidContentTypeEndpointsDefault()
         $this->assertTrue($retriever->confirmMediaType($mock, 'https://json-schema.org/'));
     }
 
-    public function testInvalidContentTypeEndpointsUnknown()
+    public function testInvalidContentTypeEndpointsUnknown(): void
     {
         $mock = $this->createMock('JsonSchema\Uri\Retrievers\UriRetrieverInterface');
         $mock->method('getContentType')->willReturn('Application/X-Fake-Type');
@@ -351,7 +351,7 @@ public function testInvalidContentTypeEndpointsUnknown()
         $retriever->confirmMediaType($mock, 'http://example.com');
     }
 
-    public function testInvalidContentTypeEndpointsAdded()
+    public function testInvalidContentTypeEndpointsAdded(): void
     {
         $mock = $this->createMock('JsonSchema\Uri\Retrievers\UriRetrieverInterface');
         $mock->method('getContentType')->willReturn('Application/X-Fake-Type');
@@ -363,7 +363,7 @@ public function testInvalidContentTypeEndpointsAdded()
         self::assertTrue($result);
     }
 
-    public function testSchemaCache()
+    public function testSchemaCache(): void
     {
         $retriever = new UriRetriever();
         $reflector = new \ReflectionObject($retriever);
@@ -382,7 +382,7 @@ public function testSchemaCache()
         );
     }
 
-    public function testLoadSchemaJSONDecodingException()
+    public function testLoadSchemaJSONDecodingException(): void
     {
         $retriever = new UriRetriever();
 
@@ -392,7 +392,7 @@ public function testLoadSchemaJSONDecodingException()
         $retriever->retrieve('package://tests/fixtures/bad-syntax.json');
     }
 
-    public function testGenerateURI()
+    public function testGenerateURI(): void
     {
         $retriever = new UriRetriever();
         $components = [
@@ -405,7 +405,7 @@ public function testGenerateURI()
         $this->assertEquals('scheme://authority/path?query#fragment', $retriever->generate($components));
     }
 
-    public function testResolveHTTP()
+    public function testResolveHTTP(): void
     {
         $retriever = new UriRetriever();
         $this->assertEquals(
@@ -414,7 +414,7 @@ public function testResolveHTTP()
         );
     }
 
-    public function combinedURITests()
+    public function combinedURITests(): array
     {
         return [
             ['blue', 'http://example.com/red', 'http://example.com/blue'],
@@ -425,13 +425,13 @@ public function combinedURITests()
     /**
      * @dataProvider combinedURITests
      */
-    public function testResolveCombinedURI($uri, $baseURI, $combinedURI)
+    public function testResolveCombinedURI($uri, $baseURI, $combinedURI): void
     {
         $retriever = new UriRetriever();
         $this->assertEquals($combinedURI, $retriever->resolve($uri, $baseURI));
     }
 
-    public function testIsValidURI()
+    public function testIsValidURI(): void
     {
         $retriever = new UriRetriever();
         $this->assertTrue($retriever->isValid('http://example.com/schema'));
diff --git a/tests/ValidatorTest.php b/tests/ValidatorTest.php
index eec59a10..26a8069d 100644
--- a/tests/ValidatorTest.php
+++ b/tests/ValidatorTest.php
@@ -7,7 +7,7 @@
 
 class ValidatorTest extends TestCase
 {
-    public function testValidateWithAssocSchema()
+    public function testValidateWithAssocSchema(): void
     {
         $schema = json_decode('{"properties":{"propertyOne":{"type":"array","items":[{"type":"string"}]}}}', true);
         $data = json_decode('{"propertyOne":[42]}', true);
@@ -18,7 +18,7 @@ public function testValidateWithAssocSchema()
         $this->assertFalse($validator->isValid(), 'Validation succeeded, but should have failed.');
     }
 
-    public function testBadAssocSchemaInput()
+    public function testBadAssocSchemaInput(): void
     {
         if (version_compare(phpversion(), '5.5.0', '<')) {
             $this->markTestSkipped('PHP versions < 5.5.0 trigger an error on json_encode issues');
@@ -35,7 +35,7 @@ public function testBadAssocSchemaInput()
         $validator->validate($data, $schema);
     }
 
-    public function testDeprecatedCheckDelegatesToValidate()
+    public function testDeprecatedCheckDelegatesToValidate(): void
     {
         $schema = json_decode('{"type":"string"}');
         $data = json_decode('42');
@@ -46,7 +46,7 @@ public function testDeprecatedCheckDelegatesToValidate()
         $this->assertFalse($validator->isValid(), 'Validation succeeded, but should have failed.');
     }
 
-    public function testDeprecatedCoerceDelegatesToValidate()
+    public function testDeprecatedCoerceDelegatesToValidate(): void
     {
         $schema = json_decode('{"type":"integer"}');
         $data = json_decode('"42"');