weird operator test: assert.operator(1, '!==', '1') #386

jokeyrhyme opened this Issue Mar 3, 2015 · 1 comment


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I just noticed a weird test for assert.operator():

    err(function () {
      assert.operator(1, '!==', '1');
     }, "expected 1 to be !== \'1\'");

Basically, this test expects the assertion to throw an error, and will throw an error (failing the test) if it does not.

!== is strict inequality, which means types should matter. Is there a special reason why the Number 1 is expected to be strictly equal to the String "1" ?


Congratulations @jokeyrhyme! You've just found a bug! Thanks very much for filing this issue - you're totally right - that isn't meant to behave that way.

After a bit of examination, it has to do with the way the operators are checked. assert.operator uses eval - and it concatenates the values together with the operator as a String. Given the example, the values Number(1), String('!==') and String('1') are concatenated (constructors used for emphasis). Of course, this makes a string of String('1 !== 1') - and so I suspect the tests have been malformed to fix what appeared to be breaking tests, but was actually breaking code.

Interestingly, this makes assert.operator especially useless for testing lots of primitive values; for example assert.operator([1,2,3], '===', [1,2,3]); becomes eval('1,2,3===1,2,3'); which returns 3, not false like it should.

I see there being two proposals for a fix:

1: Trick the eval function into using strings.

We want the eval function to get literal values wrapped in their correct syntax. The easiest way to do this is to simply call JSON.stringify on each value - which will give you the equivalent JS syntax for that literal, as a String. E.g. JSON.stringify(Number(1)) === '1' while JSON.stringify(String(1)) === '"1"'. So Line 1010 of assert.js becomes:

var test = new Assertion(eval(JSON.stringify(val) + operator + JSON.stringify(val2)), msg);

2: Stop using eval

Probably the better fix for this is to just stop using eval - the code will be longer but potentially more reliable and less prone to bugs like these. Of course, this means the laborious task of taking each operator and making the appropriate statement in JS. For example:

switch(operator) {
case '===':
    ok = val1 === val2;
case '!==':
    ok = val1 !== val2;
// and so on

The nice benefit to this is that references are kept (they wouldn't have been with eval) so asserts like: assert.operator(x, '===', x); (where x is not a primitive) also work.

Ultimately I feel like solution 2 is the correct one - if you'd like to make a PR @jokeyrhyme, I'd be happy to review and merge it. If you do so - make sure you add a good few tests, especially if you do end up implementing solution 2 - also add some tests around asserting references, as mentioned above. Getting a PR merged is basically the best feeling ever, and lands you a place on our contributors hall of fame, and if you get stuck I'll be on point to help out if needed.

@cjqed cjqed added a commit to cjqed/chai that referenced this issue Mar 8, 2015
@cjqed cjqed No longer using eval on assert operator #386 4e16997
@cjqed cjqed added a commit to cjqed/chai that referenced this issue Mar 8, 2015
@cjqed cjqed No longer using eval on assert operator #386 da2ec4a
@keithamus keithamus closed this Mar 14, 2015
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