Travis CI with multiple database engines

.travis.yml

language: ruby

rvm:
  - 1.9.3

env:
  - DB=sqlite
  - DB=mysql
  - DB=postgresql

script:
  - RAILS_ENV=test bundle exec rake --trace db:migrate test

before_script:
  - mysql -e 'create database chromotype_test'
  - psql -c 'create database chromotype_test' -U postgres

database.yml

sqlite: &sqlite
  adapter: sqlite3
  database: db/<%= Rails.env %>.sqlite3

mysql: &mysql
  adapter: mysql2
  username: root
  password:
  database: <%= Rails.root.basename.to_s %>_<%= Rails.env %>

postgresql: &postgresql
  adapter: postgresql
  username: postgres
  password:
  database: <%= Rails.root.basename.to_s %>_<%= Rails.env %>
  min_messages: ERROR

defaults: &defaults
  pool: 5
  timeout: 5000
  host: localhost
  <<: *<%= ENV['DB'] || "postgresql" %>

development:
  <<: *defaults

test:
  <<: *defaults

production:
  <<: *defaults
  # Change this to erb-echo the production password from /etc/something here.