diff --git a/actionmailer/lib/action_mailer/test_case.rb b/actionmailer/lib/action_mailer/test_case.rb
index 80f323873d..207f949fe2 100644
--- a/actionmailer/lib/action_mailer/test_case.rb
+++ b/actionmailer/lib/action_mailer/test_case.rb
@@ -10,13 +10,6 @@ module ActionMailer
   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
 
diff --git a/actionpack/lib/action_controller/test_case.rb b/actionpack/lib/action_controller/test_case.rb
index 7b48870090..331d15d403 100644
--- a/actionpack/lib/action_controller/test_case.rb
+++ b/actionpack/lib/action_controller/test_case.rb
@@ -360,13 +360,6 @@ module ActionController
   #
   #  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
diff --git a/actionpack/lib/action_dispatch/testing/integration.rb b/actionpack/lib/action_dispatch/testing/integration.rb
index 95cd89a166..1fc5933e98 100644
--- a/actionpack/lib/action_dispatch/testing/integration.rb
+++ b/actionpack/lib/action_dispatch/testing/integration.rb
@@ -491,9 +491,6 @@ module ActionDispatch
     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
diff --git a/actionpack/lib/action_view/test_case.rb b/actionpack/lib/action_view/test_case.rb
index a548b44780..4479da5bc4 100644
--- a/actionpack/lib/action_view/test_case.rb
+++ b/actionpack/lib/action_view/test_case.rb
@@ -30,9 +30,6 @@ module ActionView
       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
 
diff --git a/activesupport/lib/active_support/test_case.rb b/activesupport/lib/active_support/test_case.rb
index be1bdbb52f..4290d5b3ed 100644
--- a/activesupport/lib/active_support/test_case.rb
+++ b/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 @@ rescue LoadError
 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__
 
diff --git a/railties/test/engine_test.rb b/railties/test/engine_test.rb
index addf49cdb6..7970913d21 100644
--- a/railties/test/engine_test.rb
+++ b/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