Decorate Rails' backtrace cleaner before passing to minitest

The minitest database cleaner never returns empty traces so we need to
make sure ours also have the same behavior before passing to minitest.

railties/lib/minitest/rails_plugin.rb

@@ -35,12 +35,24 @@ module Minitest
     options[:output_inline] = true
   end
 
+  class RailsBacktraceCleanerDecorator
+    def initialize(backtrace_cleaner)
+      @backtrace_cleaner = backtrace_cleaner
+    end
+
+    def filter(backtrace)
+      filtered = @backtrace_cleaner.filter(backtrace)
+      filtered = backtrace.dup if filtered.empty?
+      filtered
+    end
+  end
+
   # Owes great inspiration to test runner trailblazers like RSpec,
   # minitest-reporters, maxitest and others.
   def self.plugin_rails_init(options)
     unless options[:full_backtrace] || ENV["BACKTRACE"]
       # Plugin can run without Rails loaded, check before filtering.
-      Minitest.backtrace_filter = ::Rails.backtrace_cleaner if ::Rails.respond_to?(:backtrace_cleaner)
+      Minitest.backtrace_filter = RailsBacktraceCleanerDecorator.new(::Rails.backtrace_cleaner) if ::Rails.respond_to?(:backtrace_cleaner)
     end
 
     # Suppress summary reports when outputting inline rerun snippets.

railties/test/application/test_runner_test.rb

@@ -514,7 +514,7 @@ module ApplicationTests
     def test_shows_filtered_backtrace_by_default
       create_backtrace_test
 
-      assert_match "Rails::BacktraceCleaner", run_test_command("test/unit/backtrace_test.rb")
+      assert_match "Minitest::RailsBacktraceCleanerDecorator", run_test_command("test/unit/backtrace_test.rb")
     end
 
     def test_backtrace_option