RSpec Nested Transactions

Creating the same records in the database for every single test in a group can slow down your suite. This is a common approach when using factories rather than fixtures loaded in suite initialization. I much prefer factories over fixtures but for a long time I employ a technique that enable a test suite to perform as well as using fixtures (or better if you're running just a few tests from the suite) and read as good as you are used to when using factories.

Some databases, like PostgreSQL, allow transaction savepoints. That means it's possible to run inner transactions inside an outer transaction to put in simple words.

So, if you were able to create a set of records in a before(:all) context and rollback those changes once the context is finished, then there would no need to recreate those records for each example in the context. If you also run each example in an inner transaction, that means the examples will be still isolated from each other with regards to the database state.

RSpec doesn't allow one to run an around hook that would include contexts besides examples.

Myron Marston wrote an article explaining how to use Ruby Fibers to implement around(:all) on RSpec. It's an interesting idea and I used the concept to implement this feature.

Requirements

The specs for this project will only run on Ruby 2.3 and above due to the <<~ heredoc usage, but I suspect it works on any Ruby >= 2.0 (due to prepend usage).

Installation

Add this line to your application's Gemfile:

gem 'rspec_nested_transactions'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rspec_nested_transactions

Usage

RSpec.configure do |c|
  c.nested_transaction do |example_or_group, run|
    (run[]; next) unless example_or_group.metadata[:db] # or delete this line if you don't care
    # With Sequel and PostgreSQL, Oracle, MS SQL Server, MySQL[InnoDB], ...:
    DB.transaction(auto_savepoint: true, savepoint: true, rollback: :always, &run)

    # With ActiveRecord:
    ActiveRecord::Base.transaction(requires_new: true) do
      run[]
      raise ActiveRecord::Rollback
    end

    # Alternatively:
    # conditionally issue a "BEGIN" or "SAVEPOINT #{dynamic_savepoint_name}"
    # run[]
    # conditionally issue a "ROLLBACK" or "ROLLBACK TO SAVEPOINT #{dynamic_savepoint_name}"
  end
end

After that every context and example will be enclosed in a (inner) transaction. No need for DatabaseCleaner (rolling back transactions are usually faster than truncate).

nested_transaction can also be called from inside describe/context groups just like around:

RSpec.describe "Some Feature" do
  nested_transaction do |example_or_group, run|
    # do something and call run[] ( or run.call/run.(), your call )
  end
end

Is it "production" safe?

Well, I've been using this technique since 2013 using my fork of rspec_around_all.

Actually I've been using it for much longer, but using some monkey patches around Sequel, before I read Myron's post. However, that code from 2013 is used to this date without changes so I consider it to be stable. That's why I decided to clean it up by removing the parts I didn't need, used a separate methods (instead of reusing around) and improved the specs to be clearer. As a result they now require Ruby 2.3 to run. Also, it now uses prepend rather than Object.instance_method(:extend).bind(c).call, which means it now requires Ruby >= 2.

I never had problems with my test database becoming inconsistents during all those years.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub.

License

The gem is available as open source under the terms of the MIT License.

rosenfeld/rspec_nested_transactions