jest async test block

[holi-java]

when run the test and expectation failed,this test will be blocked until timeout,not failed immediately.

test('expect failed immediately in async test', (done) => {
    setTimeout(() => {
        expect(false).toBe(true);
        done();
    });
});

[lund0n]

@holi-java The expect() call with throw an error due to the assertion failing, causing the done() call to be skipped. Since done() never gets called, Jest will not know whether the test succeeds or fails until the timeout is hit.

Wrapping the code inside of the setTimeout() function is one way to handle this, like so:

test('expect failed immediately in async test', done => {
	setTimeout(() => {
		try {
			expect(false).toBe(true)
			done()
		} catch (err) {
			done.fail(err)
		}
	})
})

The assertion error is caught, with the error being passed to Jest using done.fail(err). This will indicate to Jest that the test is done running, mark it as an failure, and report what it failed on.

[holi-java]

@lund0n thanks,but I think this way is not perfect,because I need using try catch structure.I found if the main thread throws any exception then the test failed immediately.why couldn't let jest do this?may be proxy setTimeout function per test to running can reach it,as TestEvironment in jest.

test('expect failed in async test if main thread throws exception', (done) => {
    expect(true).toBe(false);
});

[thymikee]

why couldn't let jest do this?

Because it's just not that simple. Every time done callback is involved we defer work to Jasmine and rely on how it handles such cases. Which is bad and we need to fix it.
Although this doesn't happen if you can return a Promise from your test (then Jest handles it and catches the error as a promise's rejection).

I'll close this, because this issue is known and we'll try to push it forward to the next release or so.
Related issues: #2059, #2136

[holi-java]

I'm sorry @thymikee,but I‘m just to tell you I can solve the problem by setupTestFrameworkScriptFile option.and ask you whether has a way to embed the code like this.

setupTestFrameworkScriptFile

const top = global || window;

let [nativeTest, _setTimeout, _setInterval, test]=[top.test, top.setTimeout, top.setInterval, function (name, currentTest) {
    if (!currentTest.length) return nativeTest(name, currentTest);
    return nativeTest(name, (done) => {
        let queue = new Set();
        let proxy = (execute) => {
            return (callback, mills, args) => {
                let tid = Symbol();
                queue.add(tid);
                return execute(() => {
                    try {
                        callback();
                        queue.delete(tid);
                    } catch (e) {
                        queue.clear();
                        done.fail(e);
                    }
                }, mills, args);
            }
        };
        top.setTimeout = proxy(_setTimeout);
        top.setInterval = proxy(_setInterval);
        try {
            currentTest(done);
        } finally {
            let timerId = _setInterval(() => {
                if (!queue.size) {
                    clearInterval(timerId);
                    global.setTimeout = _setTimeout;
                    global.setTimeout = _setInterval;
                }
            });
        }
    });
}];
top.it = top.test = test;

async test js

test('expect failed in async test failed immediately', (done) => {
    setTimeout(() => {
        setTimeout(() => {
            expect(false).toBe(true);
            done();
        });
    })
});

[dfroger]

The solution proposed by @holi-java with setupTestFrameworkScriptFile is the only way I've found to test with jest code that may raise an error in a setTimeout.

@thymikee any chance somthing like that could be integrated into the core of jest? Isn't it a problem that for some function (which raise error in a setTimeout) that are unit-tested, jest just don't work, and to do no report the error?

Should we start a PR?

[thymikee]

@dfroger this is already supported in latest test version od Jest. You can give it a shot: yarn add jest@test --dev

[dfroger]

@thymikee works perfectly, awesome! (thanks for your quick reply, didn't noticed it was already supported in lasted test).

[dfroger]

for reference, fixed in #4669

[zamber]

Expanding on @lund0n 's approach, I did a simple helper for testing chained callbacks:

// https://github.com/facebook/jest/issues/2980
// otherwise if an assertion fails we will get a timeout
// without any feedback about which assertion threw
const assertInCallback = (done) => {

    // without the tracker the test fill PASS on first callback with good assertions
    const successTracker = {};
    setTimeout(() => {
        Object.keys(successTracker)
            .filter((cbID) => !!successTracker[cbID])
            .forEach((failure) => done.fail(successTracker[failure]));
        done();
    }, 4500 ); // default timeout for jest is 5s, adjust if needed

    return (func) => {
        return function() { // we need arguments
            const id = (new Date).getTime();
            successTracker[id] = undefined;
            try {
                return func(...arguments); // not sure if return needed here
            } catch (e) {
                successTracker[id] = e;
            }
        };
    };
};

describe('ThingWithChainableCallbacks', () => {

    it('works', done => {
        const a = assertInCallback(done);
        (new ThingWithChainableCallbacks(data))
            .onprogress(a((progressEvent) => {
                expect(progressEvent.lengthComputable).toBe(true);
                expect(progressEvent.loaded).toBe(1337);
                expect(progressEvent.total).toBe(1337);
            }))
            .parse(a((result) => {
                expect(result).toMatchObject([ 'nice ]);
            }));
    });

});

Hopefully it will save time someone who finds this issue as I did :).

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