Learn how to test React applications with the Jest JavaScript testing framework.

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MockingJest allows you to mock objects in your test files. You can turn on automatic mocking with automock which will mock every component/object that the component is part of your project. For the first test, we'll write a simple test that ensures that Jest was set up correctly and that it can run a test successfully.

Testing React Applications with Jest

does anyone actually test their React applications at the component level? please leave a comment.
I remember using the Jest test runner professionally (along with Enzyme for UI testing and Sinon for spies, stubs, and mocks).
but, what I’ve found is that real-world applications are not testable. they lack SOLID principles and they are so monolithic and tightly-coupled that it’s not possible to achieve good test coverage.
this article is cute, theoretical, and informative, but unrealistic.
the first thing is to learn about testable code and how to refactor to make things testable (because, let’s be honest - nobody writes tests first, as TDD advises. oftentimes, especially in the professional world, testing is just an afterthought. so, you end up having to write tests against nasty piles of existing code that were written without any regard for testability or reusability. this means that you must overextend yourself and fight with ugly code just to even author simple tests. it’s a huge pain in the neck that nobody, except hobbyists &amp; purists, wants to deal with.)
also, keep in mind that real-world applications change frequently to meet business demands. so, leadership doesn’t want to invest time implementing unit tests, because they’ll break next quarter, when the company makes changes to pursue some new initiative. you effectively end up managing two code bases, and it’s not worth the headache.
unit testing is more appropriate when building reusable frameworks, plugins, and libraries, not toy applications and certainly not real-world applications.