Migrating to Jest test runner

I have already shared my comparison of two JavaScript testing solutions where I admitted that I favor Jest over Mocha. Back then, I listed all major differences between those tools summarized with advantages and disadvantages of migrating to Jest:

Pros:

  • Simpler API, less boilerplate code.
  • Flexible and easy configuration.
  • Test files executed in isolation.
  • Advanced watch mode.
  • Snapshots support = easier start with testing.
  • Code coverage.

Cons:

  • Another migration.
  • Mocha has still a bit better performance (according to my quick tests).

My analysis got very positive feedback, with only a few little concerns, so I got encouraged to take action and verify the assumptions stated. I picked two different projects to play with to ensure both of them will uniformly benefit from using Jest.

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Picking Jest over Mocha – testing tools comparison

At Automattic we use Mocha to run all tests written for Calypso project which powers WordPress.com. It also includes end-to-end tests, which live in their own repository. We have been using this setup for over 3 years now. I think it is a good moment to revisit this choice. I found this unit testing tools comparison very helpful when evaluating alternatives. I strongly agree with the conclusions shared by Martin Olsson in his article:

Staying with Javascript, I think it’s hard to ignore the momentum behind Jest. I would be awesome if someone fixed #2059 though. Then again, Mocha seems to work well enough for a lot of people.

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