Add test-unit as a development dependency

activemerchant.gemspec

@@ -28,6 +28,7 @@ Gem::Specification.new do |s|
   s.add_dependency("offsite_payments", "~> 2.0.0")
 
   s.add_development_dependency('rake')
+  s.add_development_dependency('test-unit', '~> 1.2.3')
   s.add_development_dependency('mocha', '~> 0.13.0')
   s.add_development_dependency('rails', '>= 3.2.14')
   s.add_development_dependency('thor')

test/test_helper.rb

@@ -1,22 +1,13 @@
 #!/usr/bin/env ruby
 $:.unshift File.expand_path('../../lib', __FILE__)
 
-begin
-  require 'rubygems'
-  require 'bundler'
-  Bundler.setup
-rescue LoadError => e
-  puts "Error loading bundler (#{e.message}): \"gem install bundler\" for bundler support."
-end
+require 'bundler/setup'
 
 require 'test/unit'
 
 require 'mocha/version'
-if(Mocha::VERSION.split(".")[1].to_i < 12)
-  require 'mocha'
-else
-  require 'mocha/setup'
-end
+require 'mocha/setup'
+
 require 'yaml'
 require 'json'
 require 'active_merchant'
@@ -47,7 +38,7 @@ class SubclassGateway < SimpleTestGateway
 
 module ActiveMerchant
   module Assertions
-    AssertionClass = RUBY_VERSION > '1.9' ? MiniTest::Assertion : Test::Unit::AssertionFailedError
+    AssertionClass = defined?(Minitest) ? MiniTest::Assertion : Test::Unit::AssertionFailedError
 
     def assert_field(field, value)
       clean_backtrace do