Rake test:uncommitted finds git directory in ancestors.

Sometimes your git directory is an ancestor of your application root
directory.

For example:
 ./repo/.git/
 ./repo/app/Rakefile

In this case rake test:uncommitted will be unable to detect your SCM.

This patch fixes this and add a test.

railties/lib/rails/test_unit/testing.rake

@@ -88,7 +88,7 @@ namespace :test do
     def t.file_list
       if File.directory?(".svn")
         changed_since_checkin = silence_stderr { `svn status` }.split.map { |path| path.chomp[7 .. -1] }
-      elsif File.directory?(".git")
+      elsif system "git rev-parse --git-dir 2>&1 >/dev/null"
         changed_since_checkin = silence_stderr { `git ls-files --modified --others --exclude-standard` }.split.map { |path| path.chomp }
       else
         abort "Not a Subversion or Git checkout."

railties/test/application/rake_test.rb

@@ -106,6 +106,35 @@ module ApplicationTests
       end
     end
 
+    def test_rake_test_uncommitted_always_find_git_in_parent_dir
+      app_name = File.basename(app_path)
+      app_dir = File.dirname(app_path)
+      moved_app_name = app_name + '_moved'
+      moved_app_path = "#{app_path}/#{moved_app_name}"
+
+      Dir.chdir(app_dir) do
+        # Go from "./app/" to "./app/app_moved"
+        FileUtils.mv(app_name, moved_app_name)
+        FileUtils.mkdir(app_name)
+        FileUtils.mv(moved_app_name, app_name)
+        # Initialize the git repository and start the test.
+        Dir.chdir(app_name) do
+          `git init`
+          Dir.chdir(moved_app_name){ `rake db:migrate` }
+          silence_stderr { Dir.chdir(moved_app_name) { `rake test:uncommitted` } }
+          assert_equal 0, $?.exitstatus
+        end
+      end
+    end
+
+    def test_rake_test_uncommitted_fails_with_no_scm
+      Dir.chdir(app_path){ `rake db:migrate` }
+      Dir.chdir(app_path) do
+        silence_stderr { `rake test:uncommitted` }
+        assert_equal 1, $?.exitstatus
+      end
+    end
+
     def test_rake_routes_calls_the_route_inspector
       app_file "config/routes.rb", <<-RUBY
         AppTemplate::Application.routes.draw do