[Fix #213] Add new cop Minitest/FileName

Closes #213

changelog/new_file_name_cop.md

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

config/default.yml

@@ -127,6 +127,11 @@ Minitest/EmptyLineBeforeAssertionMethods:
   Enabled: pending
   VersionAdded: '0.23'
 
+Minitest/FileName:
+  Description: 'Checks if test file names start with `test_` or end with `_test.rb`.'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+
 Minitest/GlobalExpectations:
   Description: 'This cop checks for deprecated global expectations.'
   StyleGuide: 'https://minitest.rubystyle.guide#global-expectations'

lib/rubocop/cop/minitest/file_name.rb

@@ -0,0 +1,39 @@
+# 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 FileName < Base
+        include MinitestExplorationHelpers
+
+        MSG = 'Test file path should end with `_test.rb`.'
+
+        def on_class(node)
+          return unless test_class?(node)
+
+          add_offense(node) unless valid_file_name?
+        end
+
+        private
+
+        def valid_file_name?
+          file_name.match?('^test_.*') || file_name.match?('.*_test\.rb$')
+        end
+
+        def file_name
+          @file_name ||= File.basename(processed_source.buffer.name)
+        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/file_name'
 require_relative 'minitest/global_expectations'
 require_relative 'minitest/literal_as_actual_argument'
 require_relative 'minitest/multiple_assertions'

test/rubocop/cop/minitest/file_name_test.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class FileNameTest < Minitest::Test
+  def test_registers_offense_for_invalid_path
+    assert_offense(<<~RUBY, 'foo.rb')
+      class FooTest < Minitest::Test
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Test file path should end with `_test.rb`.
+      end
+    RUBY
+  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