What to expect when you're expecting

[astorije]

I was making tests trying to be right on #496 (:smile:) and found that if you assert:

expect(3).to.include(2);

You end up with:

     TypeError: undefined is not a function
      at Assertion.include (lib/chai/core/assertions.js:217:30)
      at Assertion.assert (lib/chai/utils/addChainableMethod.js:83:49)
      at Context.<anonymous> (test/expect.js:1131:18)

The assert.include(3, 2); twin assertion reacts similarly, but the key difference is that the assert.include(haystack, needle) method definition explicitly says that the haystack should be {Array|String} (so one just needs to read the doc). The type of the argument given to expect() is never specified in the doc (or at least I couldn't find it), meaning this should Mixed.

Making sure the type is controlled for expect(...).to.include(...) is similar to issue #491 and PR #496.

I am guessing there are other cases like that but I haven't tested them all. I am not sure if there should be a global way to do that in the code or if we should handle that on a case-by-case basis as what we are leaning to on #496.

[keithamus]

Good call as usual @astorije. We should check for other primitives in assertions like these.

I think for these kind of assertions we should probably throw an error explaining the problem. In this instance maybe AssertionError: expected 3 to include 2, but cannot include multiple values or something. Thoughts?

[astorije]

What do you mean by cannot include multiple values?

I would go for something simple and explicit like AssertionError: argument of expect() must be an Array or a String, number given (or 3 given).
It's not necessary or useful to remind the value (2) as this is not causing any error and therefore can be misleading.

What do you think?

(Depending on when we reach a decision and how much work is needed/how much time I have, I'll see if I can work on a PR or not)

[keithamus]

Agree, yours sounds much better than mine. 3 given I think would be best. PR welcome 😄

[astorije]

Okay, I'll see if I can find an hour to send you that within the next few of days. I'd personally prefer [type] given as a user, but it's up to you.

[berkerpeksag]

This is also fixed in d7d9420 (just pasting the merge commit) and can be closed now.