infinite loop when DOM mutation happens in waitFor callback

Jest hangs on the following sample test:

const { waitFor } = require("@testing-library/dom");

describe("test", () => {
  it("test", async () => {
    let value = 1;

    setTimeout(() => {
      value = 2;
    });

    await waitFor(() => {
      // both these lines are important: it's necessary to do a mutation and to fail in the first iteration
      // It works normally, if we comment one of these lines
      document.body.setAttribute("data-something", 'whatever');
      expect(value).toEqual(2);
    });

    console.log("execution never comes here");
  });
});

Two conditions have to be met:

• there should be a DOM mutation in waitFor callback
• first execution of waitFor callback should fail

Expected result: waitFor should resolve the promise after a successful iteration regardless whether there were DOM mutations or not

Current result: waitFor calls the callback infinitely even if subsequent iterations don’t throw any exception.

Environment: @testing-library/dom@7.26.4 jest@26.6.2

[ryuuji3]

The very first step of waitFor with or without fake timers is to check the callback. (https://github.com/testing-library/dom-testing-library/blob/master/src/wait-for.js#L56 or https://github.com/testing-library/dom-testing-library/blob/master/src/wait-for.js#L96) waitFor doesn’t consider booleans, its either callback throws (try again) or doesn’t throw (success). (https://github.com/testing-library/dom-testing-library/blob/master/src/wait-for.js#L146) If you need to verify against boolean then your callback should use toBeTruthy() eg.

await waitFor(() => expect(condition).toBeTruthy())

[SerkanSipahi]

I do not really understand how await waitFor(() => false); console.log('Foo') work. In my case waitFor waits for nothing. No matter if the result of the callback is true or false, the promise (waitFor) will always be resolved and Foo is logged. Have I understood something wrong here?

some env infos:

• real browser with karma + jasmine.
• angular extension of the testing-library. – waitFor is re-exported from testing-library. Therefore the issue should be reported here 👍