Eslam Hefnawy
Jun 1, 2020 ⋅ 5 min read

Testing state changes in React functional components

Eslam Hefnawy Serverless Architect at Serverless, Inc. Co-creator of the Serverless Framework and the lead architect of Serverless Components.

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6 Replies to "Testing state changes in React functional components"

  1. with this approach we need to interact with the component’s DOM and simulate the events which I feel like E2E test. I feel uncomfortable to see ‘find’ in unit tests. What do you say?

  2. Hello, I think the approach used for “should update state on click” is not correct. jest.fn() returns a function. So changeSize is a function. So changeSize will always be truthy even if you did not simulate the click. try to expect(changeSize).toBeCalled(). You will see that the function is not called at all.

  3. Big “No” on that last test. If you comment out the simulate(“click”) line in the testcase, the test still passes. Therefore this is not a valid test. As Omar said, jest.fn() returns a function. I’m surprised you didn’t update this article after his comment, which is clearly correct. I don’t recommend using a unit test to test internal state. Instead test external effects.

  4. That’s a good catch! Sorry for the confusion folks! I updated the article, notified the editors and it should be published soon.

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