Add backtrace cleaner on test unit railtie.

activesupport/lib/active_support/test_case.rb

@@ -21,12 +21,6 @@ class TestCase < ::Test::Unit::TestCase
       alias_method :method_name, :name if method_defined? :name
       alias_method :method_name, :__name__ if method_defined? :__name__
     else
-      # TODO: Figure out how to get the Rails::BacktraceFilter into minitest/unit
-      if defined?(Rails) && ENV['BACKTRACE'].nil?
-        require 'rails/backtrace_cleaner'
-        Test::Unit::Util::BacktraceFilter.module_eval { include Rails::BacktraceFilterForTestUnit }
-      end
-
       Assertion = Test::Unit::AssertionFailedError
 
       require 'active_support/testing/default'

railties/lib/rails/test_unit/railtie.rb

@@ -13,5 +13,13 @@ class TestUnitRailtie < Rails::Railtie
     rake_tasks do
       load "rails/test_unit/testing.rake"
     end
+
+    initializer "test_unit.backtrace_cleaner" do
+      # TODO: Figure out how to get the Rails::BacktraceFilter into minitest/unit
+      unless defined?(Minitest) || ENV['BACKTRACE']
+        require 'rails/backtrace_cleaner'
+        Test::Unit::Util::BacktraceFilter.module_eval { include Rails::BacktraceFilterForTestUnit }
+      end
+    end
   end
 end
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