Fix Gemfile dependencies for Rails 4.1 and use Minitest if available

Fallback to test/unit in case minitest is not available, which should be
necessary for Ruby 1.8.7 only.

gemfiles/Gemfile.rails-4.1.x

@@ -2,7 +2,7 @@ source 'https://rubygems.org'
 
 gemspec :path => '..'
 
-gem 'activesupport', '~> 4.0.0'
+gem 'activesupport', '~> 4.1.0'
 gem 'mocha'
 gem 'test_declarative'
 gem 'rufus-tokyo'

gemfiles/Gemfile.rails-4.1.x.lock

@@ -6,29 +6,30 @@ PATH
 GEM
   remote: https://rubygems.org/
   specs:
-    activesupport (4.0.5)
+    activesupport (4.1.1)
       i18n (~> 0.6, >= 0.6.9)
-      minitest (~> 4.2)
-      multi_json (~> 1.3)
+      json (~> 1.7, >= 1.7.7)
+      minitest (~> 5.1)
       thread_safe (~> 0.1)
-      tzinfo (~> 0.3.37)
+      tzinfo (~> 1.1)
     ffi (1.9.3)
+    json (1.8.1)
     metaclass (0.0.4)
-    minitest (4.7.5)
+    minitest (5.3.3)
     mocha (1.0.0)
       metaclass (~> 0.0.1)
-    multi_json (1.10.0)
     rake (10.3.1)
     rufus-tokyo (1.0.7)
     test_declarative (0.0.5)
     thread_safe (0.3.3)
-    tzinfo (0.3.39)
+    tzinfo (1.1.0)
+      thread_safe (~> 0.1)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
-  activesupport (~> 4.0.0)
+  activesupport (~> 4.1.0)
   ffi
   i18n!
   mocha

test/test_helper.rb

@@ -1,7 +1,25 @@
 $KCODE = 'u' if RUBY_VERSION <= '1.9'
 
 require 'rubygems'
-require 'test/unit'
+
+# Use minitest if we can, otherwise fallback to test-unit.
+begin
+  require 'minitest/autorun'
+  TEST_CASE = defined?(Minitest::Test) ? Minitest::Test : MiniTest::Unit::TestCase
+
+  # TODO: Remove these aliases and update tests accordingly.
+  class TEST_CASE
+    alias :assert_raise :assert_raises
+    alias :assert_not_equal :refute_equal
+
+    def assert_nothing_raised(*args)
+      yield
+    end
+  end
+rescue LoadError
+  require 'test/unit'
+  TEST_CASE = Test::Unit::TestCase
+end
 
 # Do not load the i18n gem from libraries like active_support.
 #
@@ -17,7 +35,7 @@ def gem(gem_name, *version_requirements)
 require 'mocha/setup'
 require 'test_declarative'
 
-class I18n::TestCase < Test::Unit::TestCase
+class I18n::TestCase < TEST_CASE
   def self.setup_rufus_tokyo
     require 'rufus/tokyo'
   rescue LoadError => e