[Fix #213] Add new cop Minitest/TestFileName

Closes #213

changelog/new_test_file_name_cop.md

@@ -0,0 +1 @@
+* [#213](https://github.com/rubocop/rubocop-minitest/issues/213): Add new `Minitest/TestFileName` cop. ([@tejasbubane][])

config/default.yml

@@ -246,6 +246,12 @@ Minitest/SkipWithoutReason:
   Enabled: pending
   VersionAdded: '0.24'
 
+Minitest/TestFileName:
+  Description: 'Checks if test file names start with `test_` or end with `_test.rb`.'
+  StyleGuide: 'https://minitest.rubystyle.guide/#file-naming'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+
 Minitest/TestMethodName:
   Description: 'This cop enforces that test method names start with `test_` prefix.'
   Enabled: 'pending'

lib/rubocop/cop/minitest/test_file_name.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Minitest
+      # Checks if test file names start with `test_` or end with `_test.rb`.
+      #
+      # @example
+      #   # bad
+      #   my_class.rb
+      #
+      #   # good
+      #   my_class_test.rb
+      #   test_my_class.rb
+      #
+      class TestFileName < Base
+        include MinitestExplorationHelpers
+
+        MSG = 'Test file path should start with `test_` or end with `_test.rb`.'
+
+        def on_new_investigation
+          return if processed_source.blank?
+          return unless test_file?(processed_source.ast)
+
+          add_global_offense(MSG) unless valid_file_name?
+        end
+
+        private
+
+        def test_file?(node)
+          test_class?(node) || node.each_child_node.any? { |child_node| test_class?(child_node) }
+        end
+
+        def valid_file_name?
+          file_name = File.basename(processed_source.buffer.name)
+          file_name.start_with?('test_') || file_name.end_with?('_test.rb')
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/minitest_cops.rb

@@ -27,6 +27,7 @@
 require_relative 'minitest/assert_truthy'
 require_relative 'minitest/duplicate_test_run'
 require_relative 'minitest/empty_line_before_assertion_methods'
+require_relative 'minitest/test_file_name'
 require_relative 'minitest/global_expectations'
 require_relative 'minitest/literal_as_actual_argument'
 require_relative 'minitest/multiple_assertions'

lib/rubocop/cop/mixin/minitest_exploration_helpers.rb

@@ -23,7 +23,7 @@ module MinitestExplorationHelpers
       private
 
       def test_class?(class_node)
-        class_node.parent_class && class_node.identifier.source.end_with?('Test')
+        class_node&.class_type? && class_node&.parent_class && class_node.identifier.source.end_with?('Test')
       end
 
       def test_case?(node)

test/rubocop/cop/minitest/test_file_name_test.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class TestFileNameTest < Minitest::Test
+  def test_registers_offense_for_invalid_path
+    offenses = inspect_source(<<~RUBY, @cop, 'foo.rb')
+      class FooTest < Minitest::Test
+      end
+    RUBY
+    message = 'Test file path should start with `test_` or end with `_test.rb`.'
+
+    assert_equal(1, offenses.size)
+    assert_equal(message, offenses.first.message)
+  end
+
+  def test_does_not_register_offense_for_files_starting_with_test
+    assert_no_offenses(<<~RUBY, 'test_foo.rb')
+      class FooTest < Minitest::Test; end
+    RUBY
+  end
+
+  def test_does_not_register_offense_for_files_ending_with_test
+    assert_no_offenses(<<~RUBY, 'foo_test.rb')
+      class FooTest < Minitest::Test; end
+    RUBY
+  end
+
+  def test_does_not_register_offense_for_non_test_classes
+    assert_no_offenses(<<~RUBY, 'foo.rb')
+      class Foo; end
+    RUBY
+  end
+end