rejectedWith false positives when passed undefined

[mgartner]

If I pass undefined to rejectedWith() I get a dangerous false-positive test.

For example:

var Errors = require('./errors');

expect(SomePromise('hello')).to.be.rejectedWith(Errors.SomeError);

If I fat-finger Errors.SomeError, to something like Errors.SomeErrro, it will be undefined, and the expectation passes, when it shouldn't. This is gives the potential for false-positives which I feel are very dangerous.

Are there any better ways of dealing with this?

[brokenbot]

Unfortunately I'm finding this issue is true with any undefined condition, all these test pass just fine

return Promise.reject('rejected').should.be.fullfilled
return Promise.reject('rejected').should.eventually.be.randomundefinedthing
return Promise.resolve('resolved').should.be.reject

[Merott]

rejectedWith also passes with a false positive for integer values, e.g:

return Promise.reject(2).should.be.rejectedWith(1);
return Promise.resolve().should.be.rejectedWith(1);

EDIT

On further investigation, I've realised that the false-positive issue is a lot more widespread than initially thought. rejectedWith also passed with a false positive when dealing with booleans:

return Promise.reject(false).should.be.rejectedWith(true);  // passes

I'm trying to fix this in my own fork, hopefully to open a PR. However, I don't understand the logic behind some of the assertions/expectations. For example, the following is a PASS, and there is a test for it, to ensure it stays that way.

return Promise.reject('a long error string').should.be.rejectedWith('error');  // passes

I'd expect the above to fail. If I wanted to test partial strings, I'd use a regex, like so:

return Promise.reject('a long error string').should.be.rejectedWith(/error/);

Can anyone explain?

[domenic]

I wonder if this is connected to #126.

For example, the following is a PASS, and there is a test for it, to ensure it stays that way.

Chai matches error strings based on substring matching, so we do the same in Chai as Promised.

[domenic]

The best fix for this and many other issues would be that described in #47 (comment)...

[keithamus]

Some early work for this has been done in chaijs/chai#470 but it needs some work to get it to a useful point. PRs welcome 😄

[evonsdesigns]

After stumbling upon this issue, it seems like the problem is just with rejectedWith. That is, if you write out its logical equivalent,

return expect(somePromise).to.be.rejected.and.to.eventually.equal(new Error('some error message'));

...it works just fine.

[mattS-H]

it also fails to behave correctly with empty strings and single characters:
return expect(result).to.be.rejectedWith("a")

[domenic]

I guess this is a dupe of #56.