[Fix rubocop#301] Add new Minitest/NoFocus cop

config/default.yml

@@ -188,6 +188,11 @@ Minitest/NoAssertions:
   Enabled: false
   VersionAdded: '0.12'
 
+Minitest/NoFocus:
+  Description: 'Checks for focused tests.'
+  Enabled: pending
+  VersionAdded: '<<next>>'
+
 Minitest/NoTestCases:
   Description: 'Checks if test class contains any test cases.'
   Enabled: false

lib/rubocop/cop/minitest/no_focus.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Minitest
+      # Enforces tests are not focused
+      #
+      # @example
+      #   # bad
+      #   focus
+      #   test 'foo' do
+      #   end
+      #
+      #   # good
+      #   test 'foo' do
+      #   end
+      #
+      class NoFocus < Base
+        MSG = 'Remove `focus` from tests.'
+        RESTRICT_ON_SEND = [:focus].freeze
+
+        def_node_matcher :focused?, <<~PATTERN
+          (send nil? :focus ...)
+        PATTERN
+
+        def on_send(node)
+          return unless focused?(node)
+
+          add_offense node
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/minitest_cops.rb

@@ -30,6 +30,7 @@
 require_relative 'minitest/assert_truthy'
 require_relative 'minitest/duplicate_test_run'
 require_relative 'minitest/empty_line_before_assertion_methods'
+require_relative 'minitest/no_focus'
 require_relative 'minitest/non_executable_test_method'
 require_relative 'minitest/redundant_message_argument'
 require_relative 'minitest/return_in_test_method'

test/rubocop/cop/minitest/no_focus_test.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require_relative '../../../test_helper'
+
+class NoFocusTest < Minitest::Test
+  def test_registers_offense_when_using_direct_focus
+    assert_offense(<<~RUBY)
+      class FooTest < Minitest::Test
+        focus test 'foo' do
+        ^^^^^^^^^^^^^^^^ Remove `focus` from tests.
+        end
+      end
+    RUBY
+  end
+
+  def test_registers_offense_when_using_indirect_focus
+    assert_offense(<<~RUBY)
+      class FooTest < Minitest::Test
+        focus
+        ^^^^^ Remove `focus` from tests.
+        test 'foo' do
+        end
+      end
+    RUBY
+  end
+
+  def test_does_not_register_offense_when_no_focus
+    assert_no_offenses(<<~RUBY)
+      class FooTest < Minitest::Test
+        test 'foo' do
+        end
+      end
+    RUBY
+  end
+end