Timeout and Promise causing "Uncaught Error" in console

I was unable to reproduce this issue in a command line project, but I was able to using the website HTML example: http://cucumber.github.io/cucumber-js/

I only changed the When part in the sample code, but it happens on Given and Then as well:

this.When(/^I increment the variable by (\d+)$/, function(number, next) {
  this.incrementBy(number);
  setTimeout(() => {
    throw 'this is an uncaught error'
    next()
  }, 1000)
});

Looking at the console when running the feature, I get the message:

Uncaught this is an uncaught error

It never goes to next(), so it take 5 seconds to finish. The same issue happens in Promise.then and also in setInterval. I also tested when returning a Promise and not passing next, but experienced the same issue.

I use Chai as my assertion library, and when I do expect(true).to.be.false, it throws and Assertion Error and normally; that gets picked up through Cucumber which properly fails the test. On the other hand, if I wrap this error in a setTimeout, setInterval, or Promise, then the Uncaught error message shows up in the console instead of Cucumber picking up on the error.

[Sawtaytoes]

I see, so I could do something like this:

asyncAssert = function(expectation, next) {
    try {
        expectation();
    } catch(err) {
        next(err.message);
    }
};

And wrap my statement like so:

asyncAssert(() => expect(err).to.not.exist, next);

Or I could use the much easier method without next:

this.Given(/^this should work$/, () => {
    return Promise.resolve()
    .then(() => {
        throw "This error is caught by cucumber.";
    });
});

I get it now. Cucumber has a promise handler which will catch any errors that I’m not already trying to catch in my Promise. I was able to break Cucumber’s error handling by adding a .catch to the promise:

this.Given(/^this should work$/, () => {
    return Promise.resolve()
    .then(() => {
        throw "This error is not caught by cucumber.";
    })
    .catch(() => console.log("I'm breaking cucumber!"));
});

And that’s how it should work since I’m specifically catching this error before sending it to Cucumber. If I returned a Promise.reject(err) in the .catch, then Cucumber could pickup that error as it’s now “uncaught” by my code:

this.Given(/^this should work$/, () => {
    return Promise.resolve()
    .then(() => {
        throw "This error is caught by cucumber.";
    })
    .catch(err => {
        console.log("I'm breaking cucumber!");
        return Promise.reject(err);
    });
});

I also verified it works with jQuery’s legacy promise (before version 3):

this.Given(/^this should work$/, () => {
    const deferred = $.Deferred();
    deferred.resolve();
    return deferred.promise()
    .done(() => {
        throw "This error is caught by cucumber.";
    });
});

Which means there’s a try-catch surrounding the execution of this.Given. So when you have an error in a setTimeout or Promise, there’s no way for Cucumber to know if there’s an exception thrown unless you explicitly tell it using next('Didn't pass assertion!'), or you give it access to the promise pointer and let the try-catch in Cucumber handler it.

Now I get it thanks!

[lock[bot]]

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