Faster Rails Tests


Editor’s Note: Our post today is from Peter Bell. Peter Bell is Founder and CTO of Speak Geek, a contract member of the GitHub training team, and trains and consults regularly on everything from JavaScript and Ruby development to devOps and NoSQL data stores.

When you start a new project, automated tests are a wonderful thing. You can run your comprehensive test suite in a couple of minutes and have real confidence when refactoring, knowing that your code has really good test coverage.

However, as you add more tests over time, the test suite invariably slows. And as it slows, it actually becomes less valuable — not more. Sure, it’s great to have good test coverage, but if your tests take more than about 5 minutes to run, your developers either won’t run them often, or will waste lots of time waiting for them to complete. By the time tests hit fifteen minutes, most devs will probably just rely on a CI server to let them know if they’ve broken the build. If your test suite exceeds half an hour, you’re probably going to have to break out your tests into levels and run them sequentially based on risk – making it more complex to manage and maintain, and substantially increasing the time between creating and noticing bugs, hampering flow for your developers and increasing debugging costs.

The question then is how to speed up your test suite. There are a several ways to approach the problem. A good starting point is to give your test suite a spring clean. Reduce the number of tests by rewriting those specific to particular stories as “user journeys”. A complex, multi-page registration feature might be broken down into a bunch of smaller user stories while being developed, but once it’s done you should be able to remove lots of the story-specific acceptance tests, replacing them with a handful of high level smoke tests for the entire registration flow, adding in some faster unit tests where required to keep the comprehensiveness of the test suite.

In general it’s also worth looking at your acceptance tests and seeing how many of them could be tested at a lower level without having to spin up the entire app, including the user interface and the database.

Consider breaking out your model logic and treating your active record models as lightweight Data Access Objects. One of my original concerns when moving to Rails was the coupling of data access and model logic and it’s nice to see a trend towards separating logic from database access. A great side effect is a huge improvement in the speed of your “unit” tests as, instead of being integration tests which depend on the database, they really will just test the functionality in the methods you’re writing.

It’s also worth thinking more generally about exactly what is being spun up every time you run a particular test. Do you really need to connect to an internal API or could you just stub or mock it out? Do you really need to create a complex hairball of properly configured objects to test a method or could you make your methods more functional, passing more information in explicitly rather than depending so heavily on local state? Moving to a more functional style of coding can simplify and speed up your tests while also making it easier to reason about your code and to refactor it over time.

Finally, it’s also worth looking for quick wins that allow you to run the tests you have more quickly. Spin up a bigger instance on EC2 or buy a faster test box and make sure to parallelize your tests so they can leverage multiple cores on developers laptops and, if necessary, run across multiple machines for CI.

If you want to ensure your tests are run frequently, you’ve got to keep them easy and fast to run. Hopefully, by using some of the practices above, you’ll be able to keep your tests fast enough that there’s no reason for your dev team not to run them regularly.

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