add db:migrate task

Rakefile

@@ -9,6 +9,13 @@ RSpec::Core::RakeTask.new
 require 'cucumber/rake/task'
 Cucumber::Rake::Task.new
 
+namespace :db do
+  desc 'Prepare sqlite database'
+  task :migrate do
+    system 'cd spec/dummy && rake db:migrate RAILS_ENV=test && rake db:migrate RAILS_ENV=development'
+  end
+end
+
 desc "Run all tests for CI"
 task "ci" => ["spec", "cucumber"]
 

Readme.markdown

@@ -371,9 +371,7 @@ For automatic decoration, check out [decorates_before_rendering](https://github.
 If it's the first time you want to run the tests, start by creating the dummy database:
 
 ```
-$ pushd spec/dummy
-$ rake db:migrate db:test:prepare
-$ popd
+$ rake db:migrate
 ```
 
 You can then run tests by executing `rake`.