Set up the test helper and Gemfile.

Now Travis will build across all the Rails-es.

Gemfile

@@ -4,3 +4,11 @@ source 'https://rubygems.org'
 gemspec
 
 gem "minitest"
+
+version = ENV["RAILS_VERSION"] || "4.0"
+
+if version == "master"
+  gem "rails", github: "rails/rails"
+else
+  gem "rails", "~> #{version}"
+end

active_model_serializers.gemspec

@@ -18,6 +18,9 @@ Gem::Specification.new do |spec|
   spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
   spec.require_paths = ["lib"]
 
+  spec.add_dependency "activesupport", ">= 3.2"
+  spec.add_dependency "rails", ">= 3.2"
+
   spec.add_development_dependency "bundler", "~> 1.6"
   spec.add_development_dependency "rake"
 end

test/test_helper.rb

@@ -0,0 +1,7 @@
+require "bundler/setup"
+
+require "active_model_serializers"
+require "active_support/json"
+
+require 'rails'
+