Make sure that the test case is run under test env

* Unset $RAILS_ENV that got set by abstract_unit to trigger the default.
* split out environment setting since Ruby 1.9.3 doesn't support inline
  ENV setting.

railties/test/application/test_runner_test.rb

@@ -7,6 +7,7 @@ class TestRunnerTest < ActiveSupport::TestCase
 
     def setup
       build_app
+      ENV['RAILS_ENV'] = nil
       create_schema
     end
 
@@ -22,6 +23,20 @@ def test_should_not_display_heading
       end
     end
 
+    def test_run_in_test_environment
+      app_file 'test/unit/env_test.rb', <<-RUBY
+        require 'test_helper'
+
+        class EnvTest < ActiveSupport::TestCase
+          def test_env
+            puts "Current Environment: \#{Rails.env}"
+          end
+        end
+      RUBY
+
+      assert_match /Current Environment: test/, run_test_command('test/unit/env_test.rb')
+    end
+
     def test_run_shortcut
       create_test_file :models, 'foo'
       output = Dir.chdir(app_path) { `bundle exec rails t test/models/foo_test.rb` }
@@ -200,7 +215,8 @@ def test_env
         end
       RUBY
 
-      assert_match /development/, Dir.chdir(app_path) { `RAILS_ENV=development bundle exec rails test test/unit/env_test.rb` }
+      ENV['RAILS_ENV'] = 'development'
+      assert_match /development/, run_test_command('test/unit/env_test.rb')
     end
 
     def test_run_different_environment_using_e_tag