refactor: Add Includes matcher class

src/PhpPact/Consumer/Matcher/Matchers/Includes.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace PhpPact\Consumer\Matcher\Matchers;
+
+use PhpPact\Consumer\Matcher\Model\MatcherInterface;
+
+/**
+ * This checks if the string representation of a value contains the substring.
+ */
+class Includes implements MatcherInterface
+{
+    public function __construct(private string $value)
+    {
+    }
+
+    /**
+     * @return array<string, string>
+     */
+    public function jsonSerialize(): array
+    {
+        return [
+            'pact:matcher:type' => $this->getType(),
+            'value'             => $this->value,
+        ];
+    }
+
+    public function getType(): string
+    {
+        return 'include';
+    }
+}

tests/PhpPact/Consumer/Matcher/Matchers/IncludesTest.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace PhpPactTest\Consumer\Matcher\Matchers;
+
+use PhpPact\Consumer\Matcher\Matchers\Includes;
+use PHPUnit\Framework\TestCase;
+
+class IncludesTest extends TestCase
+{
+    public function testSerialize(): void
+    {
+        $string = new Includes('contains this string');
+        $this->assertSame(
+            '{"pact:matcher:type":"include","value":"contains this string"}',
+            json_encode($string)
+        );
+    }
+}