Writing Custom Matchers
Discover how to create custom matchers in Jest to extend testing capabilities beyond native tools. Learn when and how to write matcher functions that evaluate complex conditions, return pass or fail statuses, and provide meaningful failure messages for your JavaScript tests.
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Our applications are nuanced and will have nuanced testing needs. If Jest and other matcher libraries don’t suffice, we have the option to actually create our own matchers.
When to write a custom matcher
The tools that we already have will get us pretty far. Native matchers should be the first thing we reach for in tests. They are high quality, reliable, easily readable, and versatile.
Custom matchers should be reserved for specific logic that isn’t easily testable with these existing tools. Ultimately, a custom matcher will still execute in the same way. It will return true or false, and it will pass or fail based on whether or not something happened. ...