_.debounce() breaks fake timers

[aldendaniels]

_.debounce() breaks fake timers

In tests, it's common to replace JS timer methods such as setTimeout and setInterval with fake methods in order to control the passage of time. See Jest Timer Mocks and Sinon Fake Timers. Doing this allows you to march the clock forward in tests, executing all timers synchronously.

Recursive calls to setTimeout pose a problem when doing this, because the recursive setTimeout calls are executed synchronously, causing infinite recursion.

[jdalton]

The latest v4 should no longer be breaking fake timers.

Dup of #2533.

[rimunroe]

I'm still seeing the same issue with it in v4.17.4 of Lodash. I tried it with Jest 18 & 19 on Node 4 & 6.

jest.useFakeTimers();

var _ = require('lodash');

test('fails to mock Lodash timers correctly', function() {
  var test = jest.fn();
  var debounced = _.debounce(test, 1000);

  debounced();
  debounced();

  jest.runAllTimers();

  expect(test).toHaveBeenCalledTimes(1);
});

Running that with Jest causes it to say "Ran 100000 timers, and there are still more! Assuming we've hit an infinite recursion and bailing out...". Do you think this is a Lodash issue, or is this something I should pursue on Jest's end?

[jdalton]

Lodash doesn't hold on to references to setTimeout, clearTimeout, or Date.now so your guess is as good as mine.

[jkettmann]

@rimunroe Did you solve your issue somehow? Having a similar problem

[rimunroe]

I ended up just avoiding using it, or actually waiting in tests when I absolutely had to. I opened jestjs/jest#3465 about the problem though.

[NickHeiner]

I believe I know what the problem with Jest is: jestjs/jest#3465 (comment).

[skyboyer]

@jdalton so what could we(library consumers) do here? do we need mocking Date.now alongside using fake timers to mock _.debounce? should it help?

[jdalton]

@skyboyer I'd go for trying to mock _.debounce.

[lock]

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