Add NoAssertions cop

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## master (unreleased)
 
+### New features
+
+* [#124](https://github.com/rubocop/rubocop-minitest/pull/124): Add new `Minitest/NoAssertions` cop. ([@ghiculescu][])
+
 ### Changes
 
 * [#129](https://github.com/rubocop/rubocop-minitest/pull/129): Drop Ruby 2.4 support. ([@koic][])

config/default.yml

@@ -118,6 +118,11 @@ Minitest/MultipleAssertions:
   VersionAdded: '0.10'
   Max: 3
 
+Minitest/NoAssertions:
+  Description: 'This cop checks for at least one assertion (or flunk) in tests.'
+  Enabled: false
+  VersionAdded: '0.12'
+
 Minitest/RefuteEmpty:
   Description: 'This cop enforces to use `refute_empty` instead of using `refute(object.empty?)`.'
   StyleGuide: 'https://minitest.rubystyle.guide#refute-empty'

docs/modules/ROOT/pages/cops.adoc

@@ -32,6 +32,7 @@ based on the https://minitest.rubystyle.guide/[Minitest Style Guide].
 * xref:cops_minitest.adoc#minitestglobalexpectations[Minitest/GlobalExpectations]
 * xref:cops_minitest.adoc#minitestliteralasactualargument[Minitest/LiteralAsActualArgument]
 * xref:cops_minitest.adoc#minitestmultipleassertions[Minitest/MultipleAssertions]
+* xref:cops_minitest.adoc#minitestnoassertions[Minitest/NoAssertions]
 * xref:cops_minitest.adoc#minitestrefuteempty[Minitest/RefuteEmpty]
 * xref:cops_minitest.adoc#minitestrefuteequal[Minitest/RefuteEqual]
 * xref:cops_minitest.adoc#minitestrefutefalse[Minitest/RefuteFalse]

docs/modules/ROOT/pages/cops_minitest.adoc

@@ -625,6 +625,38 @@ end
 | Integer
 |===
 
+== Minitest/NoAssertions
+
+|===
+| Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
+
+| Disabled
+| Yes
+| No
+| 0.12
+| -
+|===
+
+This cop checks if test cases contain any assertion calls.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+class FooTest < Minitest::Test
+  def test_the_truth
+  end
+end
+
+# good
+class FooTest < Minitest::Test
+  def test_the_truth
+    assert true
+  end
+end
+----
+
 == Minitest/RefuteEmpty
 
 |===

lib/rubocop/cop/minitest/no_assertions.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Minitest
+      # This cop checks if test cases contain any assertion calls.
+      #
+      # @example
+      #   # bad
+      #   class FooTest < Minitest::Test
+      #     def test_the_truth
+      #     end
+      #   end
+      #
+      #   # good
+      #   class FooTest < Minitest::Test
+      #     def test_the_truth
+      #       assert true
+      #     end
+      #   end
+      #
+      class NoAssertions < Base
+        include MinitestExplorationHelpers
+
+        MSG = 'Test case has no assertions.'
+
+        def on_class(class_node)
+          return unless test_class?(class_node)
+
+          test_cases(class_node).each do |node|
+            assertions_count = assertions_count(node)
+
+            next if assertions_count.positive?
+
+            add_offense(node.block_type? ? node.loc.expression : node.loc.name)
+          end
+        end
+
+        private
+
+        def assertions_count(node)
+          base = assertion?(node) ? 1 : 0
+          base + node.each_child_node.sum { |c| assertions_count(c) }
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/minitest_cops.rb

@@ -23,6 +23,7 @@
 require_relative 'minitest/global_expectations'
 require_relative 'minitest/literal_as_actual_argument'
 require_relative 'minitest/multiple_assertions'
+require_relative 'minitest/no_assertions'
 require_relative 'minitest/refute_empty'
 require_relative 'minitest/refute_false'
 require_relative 'minitest/refute_equal'

lib/rubocop/cop/mixin/minitest_exploration_helpers.rb

@@ -19,6 +19,8 @@ module MinitestExplorationHelpers
         refute_respond_to refute_same
       ].freeze
 
+      FLUNK = 'flunk'
+
       LIFECYCLE_HOOK_METHODS = %i[
         before_setup
         setup
@@ -42,8 +44,8 @@ def test_case?(node)
       end
 
       def test_cases(class_node)
-        class_def_nodes(class_node)
-          .select { |def_node| test_case_name?(def_node.method_name) }
+        (class_def_nodes(class_node).select { |def_node| test_case_name?(def_node.method_name) }) +
+          test_method_calls(class_node)
       end
 
       def lifecycle_hooks(class_node)
@@ -62,6 +64,11 @@ def class_def_nodes(class_node)
         end
       end
 
+      # support https://api.rubyonrails.org/classes/ActiveSupport/Testing/Declarative.html
+      def test_method_calls(class_node)
+        class_node.each_child_node(:block).select { |blk| blk.each_child_node(:send).first&.method_name.to_s == 'test' }
+      end
+
       def test_case_name?(name)
         name.to_s.start_with?('test_')
       end
@@ -82,11 +89,14 @@ def assertions(def_node)
 
       def assertion?(node)
         node.send_type? &&
-          ASSERTION_PREFIXES.any? { |prefix| node.method_name.to_s.start_with?(prefix) }
+          ASSERTION_PREFIXES.any? do |prefix|
+            method_name = node.method_name.to_s
+            method_name == FLUNK || method_name.start_with?(prefix)
+          end
       end
 
       def assertion_method?(method_name)
-        ASSERTION_METHODS.include?(method_name)
+        method_name == FLUNK || ASSERTION_METHODS.include?(method_name)
       end
 
       def lifecycle_hook_method?(node)

test/rubocop/cop/minitest/no_assertions_test.rb

@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class NoAssertionsTest < Minitest::Test
+  def test_registers_offense_when_no_assertions
+    assert_offense(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_the_truth
+            ^^^^^^^^^^^^^^ Test case has no assertions.
+        end
+      end
+    RUBY
+  end
+
+  def test_registers_offense_when_no_assertions_in_block_form
+    assert_offense(<<~RUBY)
+      class FooTest < Minitest::Test
+        test "the truth" do
+        ^^^^^^^^^^^^^^^^^^^ Test case has no assertions.
+        end
+      end
+    RUBY
+  end
+
+  def test_register_no_offense_if_test_has_assertion
+    assert_no_offenses(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_the_truth
+          assert true
+        end
+      end
+    RUBY
+  end
+
+  def test_register_no_offense_for_unrelated_methods
+    assert_no_offenses(<<~RUBY)
+      class FooTest < Minitest::Test
+        def foo_bar
+          puts "this isn't a test"
+        end
+      end
+    RUBY
+  end
+
+  def test_register_no_offense_for_unrelated_blocks
+    assert_no_offenses(<<~RUBY)
+      class FooTest < Minitest::Test
+        foo "bar" do
+          puts "this isn't a test"
+        end
+      end
+    RUBY
+  end
+
+  def test_register_no_offense_if_test_flunks
+    assert_no_offenses(<<~RUBY)
+      class FooTest < Minitest::Test
+        def test_the_truth
+          flunk
+        end
+      end
+    RUBY
+  end
+end