Enable testing against multiple Rails versions

.travis.yml

@@ -4,6 +4,10 @@ rvm:
   - rbx-19mode
   - jruby-19mode
   - ruby-head
+env:
+  - "RAILS_VERSION=3.2"
+  - "RAILS_VERSION=3.1"
+  - "RAILS_VERSION=3.0"
 matrix:
   allow_failures:
     - rvm: ruby-head

Gemfile

@@ -10,3 +10,14 @@ platforms :jruby do
   gem "minitest", ">= 3.0"
   gem "activerecord-jdbcsqlite3-adapter", "~> 1.2.2.1"
 end
+
+case ENV["RAILS_VERSION"]
+when "master"
+  gem "rails", github: "rails/rails"
+when "3.2", nil
+  gem "rails", "~> 3.2.0"
+when "3.1"
+  gem "rails", "~> 3.1.0"
+when "3.0"
+  gem "rails", "~> 3.0.0"
+end