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Getting Started with Testing

Unit Testing

NewsKit uses Jest and React Testing Library for unit testing.

There is an existing memory leak issue with Jest. See Memory Leak in Jest. If your tests are running slow using Jest, we recommended that you try the following arguments:


This allows us to manually trigger garbage collection in Node.


Logs the heap usage after every test. When used together with --expose-gc, in the current version of Jest, it will force Node.js to swipe all known unused memory for each run of test.


Node sets the memory limit (--max-old-space-size=) per worker, and this command specifies the maximum number of workers the worker-pool will spawn for running tests. Currently, we set maxWorkers to 4 locally and maxWorkers to 2 in CI.


Force Jest to exit after all tests have completed running. This is useful when resources set up by test code cannot be adequately cleaned up. Jest suggested using --detectOpenHandles to help track down the external resources in use. It is advised to tear down external resources after each test to make sure Jest can shut down cleanly.

Snapshot testing

We recommend using @emotion/jest to do snapshot testing in your project, see documentation