Inherit from MiniTest::Unit::TestCase instead of MiniTest::Spec

actionmailer/lib/action_mailer/test_case.rb

@@ -10,13 +10,6 @@ def initialize(name)
  end

  class TestCase < ActiveSupport::TestCase

    # Use AM::TestCase for the base class when describing a mailer
    register_spec_type(self) do |desc|
      Class === desc && desc < ActionMailer::Base
    end
    register_spec_type(/Mailer( ?Test)?\z/i, self)

    module Behavior
      extend ActiveSupport::Concern

actionpack/lib/action_controller/test_case.rb

@@ -360,13 +360,6 @@ def exists?
  #
  #  assert_redirected_to page_url(title: 'foo')
  class TestCase < ActiveSupport::TestCase

    # Use AC::TestCase for the base class when describing a controller
    register_spec_type(self) do |desc|
      Class === desc && desc < ActionController::Metal
    end
    register_spec_type(/Controller( ?Test)?\z/i, self)

    module Behavior
      extend ActiveSupport::Concern
      include ActionDispatch::TestProcess

actionpack/lib/action_dispatch/testing/integration.rb

@@ -491,9 +491,6 @@ class IntegrationTest < ActiveSupport::TestCase
    include ActionController::TemplateAssertions
    include ActionDispatch::Routing::UrlFor

    # Use AD::IntegrationTest for acceptance tests
    register_spec_type(/(Acceptance|Integration) ?Test\z/i, self)

    @@app = nil

    def self.app

actionpack/lib/action_view/test_case.rb

@@ -30,9 +30,6 @@ def initialize
      end
    end

    # Use AV::TestCase for the base class for helpers and views
    register_spec_type(/(Helper|View)( ?Test)?\z/i, self)

    module Behavior
      extend ActiveSupport::Concern

activesupport/lib/active_support/test_case.rb

@@ -1,5 +1,5 @@
gem 'minitest' # make sure we get the gem, not stdlib
require 'minitest/spec'
require 'minitest/unit'
require 'active_support/testing/tagged_logging'
require 'active_support/testing/setup_and_teardown'
require 'active_support/testing/assertions'
@@ -17,13 +17,7 @@
end

module ActiveSupport
  class TestCase < ::MiniTest::Spec

    # Use AS::TestCase for the base class when describing a model
    register_spec_type(self) do |desc|
      Class === desc && desc < ActiveRecord::Base
    end

  class TestCase < ::MiniTest::Unit::TestCase
    Assertion = MiniTest::Assertion
    alias_method :method_name, :__name__

railties/test/engine_test.rb

@@ -1,7 +1,7 @@
require 'abstract_unit'

class EngineTest < ActiveSupport::TestCase
  it "reports routes as available only if they're actually present" do
  test "reports routes as available only if they're actually present" do
    engine = Class.new(Rails::Engine) do
      def initialize(*args)
        @routes = nil