Jest react testing: Check state after delay

while jest can run async code easily, you can use promise and setTimeout combination to wait a bit. For example this code will wait for 2 seconds:

await new Promise((r) => setTimeout(r, 2000));

Full sample test. Don't forget to add async flag before the callback function:

test('some test title', async () => {  const foo = true;  await new Promise((r) => setTimeout(r, 2000));  expect(foo).toBeDefined();});

Also, keep in mind that default "timeout" is 5 seconds (5000ms). If your test may run longer, you can add jest.setTimeout(30000); above the test(). 30000 will make sure to not timeout for 30 seconds. You can add any number you need. Full example with setTimeout:

jest.setTimeout(30000);test('some test title', async () => {  const foo = true;  await new Promise((r) => setTimeout(r, 2000));  expect(foo).toBeDefined();});

I haven't really tested this code. But, something similar to this should work I think.

const fruits = ['banana', 'apple', 'orange', 'vodka', 'kiwi'];it('mock setTimeout test', () => { jest.useFakeTimers(); setTimeout(() => {   expect(component.state().fruits).toEqual(fruits); }, 1500); jest.runAllTimers();});

You don't need to delay your tests, simply calling jest.runAllTimers() before asserting, will work.

const fruits = ['banana', 'apple', 'orange', 'vodka', 'kiwi'];it('initializes the fruits state', () => { jest.useFakeTimers(); jest.runAllTimers(); expect(component.state().fruits).toEqual(fruits);});

You could also call useFakeTimers() in a beforeEach if you are going to test multiple times and also runAllTimers() could be inside another beforeEach so you don't repeat yourself.