Today I decided to verify if Machinist could be a good replacement for Factory Girl. In our project, we have a big problem with Factory Girl: even if you tell her not to hit the database, using the Factory.build method, if an object has associations, these are saved on the DB. And this causes a huge slowdown in specs using factories. We've been using Factory Girl for nearly two years, and if we could find a way to stop him hitting the DB, we could really have a huge improvent in our test suite running time.
To verify if Machinist could perform better, I set up a basic rails app. Look at this example:
If you do a tail -f log/test.log and you run this spec, you'll see something like this:
The Factory.build method has to save dependencies on the DB to set the foreign keys on the objects and validate them.
Let's try with machinist:
This time, running tail on the test.log file and running the spec, doesn't shown any DB hit, and of yeah, we have a green test.
I verified this also by putting a debugger line after the validation and inspecting the DB from within the debugger after the validation has run - with FactoryGirl, it revealed an Address object saved on the DB, while with Mechanist it didn't.
I still haven't looked inside machinist to show how it handles this, but I'll do it soon, so keep in touch!