For rejected promises that were expected to be fulfilled, log the error that was thrown

[JaKXz]

  1) my project's component A should do something asynchronous:
     AssertionError: expected promise to be fulfilled but it was rejected with { Object (type, filename, ...) }

  2) my project's component B should do another asynchronous thing:
     AssertionError: expected promise to be fulfilled but it was rejected with { Object (type, filename, ...) }

It would be great if those printed the entire error object, just like when I add the catch block to my code to debug:

.then (data) -> doStuff data
.catch (error) -> console.log error

Apologies if this has been discussed already / is implemented and I just can't find it on the docs.

[keithamus]

(@domenic this looks to be the same kind of issue as chaijs/sinon-chai#67).

From a quick glance, I think we could get this diffing properly by just passing true as an additional argument into assertion.assert on lines 76 and 80. I'm not sure if any extra work is involved - but I'd say @JaKXz if you're up for making a PR, give that a go and see if it does what you want 😄.

[JaKXz]

@keithamus I tried that locally - passing in true for the Assertion.prototype.assert method's showDiff parameter, but it didn't seem to work :(

        function assertIfNegated(assertion, message, extra) {
            assertion.assert(true, null, message, extra.expected, extra.actual, true);
        }

        function assertIfNotNegated(assertion, message, extra) {
            assertion.assert(false, message, null, extra.expected, extra.actual, true);
        }

I also noticed that config API has showDiff set to true already, and I don't think I've changed it anywhere in my project, so unless my understanding of the "diff" is wrong, I think there might be more work involved? Not 100% sure, will keep poking around.

[keithamus]

@JaKXz it's worth reading chaijs/sinon-chai#67 as it offers a bit more context about the showDiff behaviour. If diffs aren't showing with true passed, then it could be that the reporter you're using doesn't output diffs. Which test runner and reporter are you using?

[tommysullivan]

I also have this problem using cucumber.js.

During testing to see if it was cucumber.js or chai-as-promised, I had two test cases:

In one test case, I simply returned a rejected promise to cucumber.js with an Error instance. This was automatically printed to the output using the toString() method of the error instance, which I verified was called on my error instance by overriding its toString. Which is what I want, the full output of the error.

In the other test case, I used chai-as-promised like so: expect(thePromise).to.eventually.be.fulfilled. In this case what I get is the type of output shown in the original issue description.

[domenic]

I'm rolling up all bugs in the category "isRejected/rejectedWith doesn't behave like Chai's error rejectors" into #166.