Prevent the test framework from being loaded in production mode

The test framework should not be autoloaded in production mode.  Before
this commit, the testing railtie would extend AS::TestCase.  This caused
AS::TestCase to be preloaded regardless of the environment in which we
were running.

This commit just moves the code that adds line filtering support in to
the test command where we actually execute the test runner.  That allows
us to maintain the line runner feature but only load the minimal amount
of code we need.

railties/lib/rails/commands/test/test_command.rb

@@ -1,5 +1,6 @@
 require "rails/command"
 require "rails/test_unit/minitest_plugin"
+require "rails/test_unit/line_filtering"
 
 module Rails
   module Command
@@ -11,6 +12,10 @@ module Rails
       def perform(*)
         $LOAD_PATH << Rails::Command.root.join("test")
 
+        # Add test line filtering support for running test by line number
+        # via the command line.
+        ActiveSupport::TestCase.extend Rails::LineFiltering
+
         Minitest.run_via[:rails] = true
 
         require "active_support/testing/autorun"

railties/lib/rails/test_unit/railtie.rb

@@ -1,5 +1,3 @@
-require "rails/test_unit/line_filtering"
-
 if defined?(Rake.application) && Rake.application.top_level_tasks.grep(/^(default$|test(:|$))/).any?
   ENV["RAILS_ENV"] ||= "test"
 end
@@ -13,10 +11,6 @@ module Rails
       c.integration_tool :test_unit
     end
 
-    initializer "test_unit.line_filtering" do
-      ActiveSupport::TestCase.extend Rails::LineFiltering
-    end
-
     rake_tasks do
       load "rails/test_unit/testing.rake"
     end

railties/test/application/runner_test.rb

@@ -43,6 +43,15 @@ module ApplicationTests
       assert_match "42", Dir.chdir(app_path) { `bin/rails runner "bin/count_users.rb"` }
     end
 
+    def test_no_minitest_loaded_in_production_mode
+      app_file "bin/print_features.rb", <<-SCRIPT
+      p $LOADED_FEATURES.grep(/minitest/)
+      SCRIPT
+      assert_match "[]", Dir.chdir(app_path) {
+        `RAILS_ENV=production bin/rails runner "bin/print_features.rb"`
+      }
+    end
+
     def test_should_set_dollar_0_to_file
       app_file "bin/dollar0.rb", <<-SCRIPT
       puts $0