rspec performance tip: only run DatabaseCleaner when needed

I have a rspec performance tip to share. Before you get all excited you should take a little test to see if it will work for you.

1. Are you using rspec 2?
2. Are you using DatabaseCleaner (or something similar)?
3. Do you have some tests that don’t touch the database?

If you answered yes to all of those questions, then you probably have something similar to this block in your spec_helper.rb.

config.before(:each) do
  DatabaseCleaner.start
end

config.after(:each) do
  DatabaseCleaner.clean
end

I’m guessing that most of us just copy and paste this when it’s needed in order to get Capybara request specs working correctly. The trouble is, these before and after blocks will apply to all of your tests that don’t need database access.

The trick is to only perform these statements when needed. Here’s how.

Update your rspec_helper.rb file to look more like this.

config.before(:each) do
  DatabaseCleaner.start if example.metadata[:db]
end

config.after(:each) do
  DatabaseCleaner.clean if example.metadata[:db]
end

Then run your test suite. You should notice some failures that weren’t there before. Those are the specs that need the database in a known state before they run. You need to add the :db => true metadata to those specs.

There are a couple ways to do that. You can do it to a single spec with

it 'should have a clean db', :db => true do
end

Or you can add it to an entire context with

context 'uses the database', :db => true do
  it 'should have a clean db' do
  end
end

And you can even add the metadata to a describe block with

describe AwesomeModel, :db => true do
end

Enjoy!