Chai: deep.equal() and deep.include() doesn't work with Error

[marian-r]

deep.equal() and deep.include() doesn't compare the object keys as I expect it to. I found the issue when upgrading to v4 as the deep.equal() works fine in v3.5. It stopped working in v4+.

Here is a code to confirm the issue: https://jsfiddle.net/wLzrucae/3/.

I tried adding error to the allowed types for include() assertion, but it still failed on comparison. Any ideas?

[meeber]

Thanks for the issue @marian-r.

The behavior of deep.equal is expected. The deep equality algorithm was rewritten for v4. Error objects are now checked for referential equality (per #608). That issue goes into detail, but essentially it was decided that if two Error objects have different stack traces, then they're not deeply equal.

The behavior of deep.include is a bug. The .include assertion should accept any object, including Error objects. The fix isn't as straightforward as adding error to the _.expectTypes check, but it is fixable.

[vieiralucas]

@meeber does this fixes it?

  function include (val, msg) {
    if (msg) flag(this, 'message', msg);

    _.expectTypes(this, [
      'array', 'error', 'object', // added error here
      'string', 'map', 'set',
      'weakset'
    ]);

    var obj = flag(this, 'object')
      , objType = _.type(obj).toLowerCase();

    // This block is for asserting a subset of properties in an object.
    if (objType === 'object' || objType === 'error') { // added error here
      var props = Object.keys(val)
        , negate = flag(this, 'negate')
        , firstErr = null
        , numErrs = 0;
....
....

[meeber]

@vieiralucas Yup that fixes the problem for error objects. I'm just wondering if the way we're using type-detect here will cause problems for other types of objects, particularly custom objects.

[shvaikalesh]

I've had the same issue with .deep.include when updating Chai to v4.

Real code (GitHub diff): link does not pass _.expectTypes because of custom @@toStringTag.

Simplified example:

expect({ a: 1 }).to.include({ a: 1 }) // pass
expect({ a: 1, [Symbol.toStringTag]: "foo" }).to.include({ a: 1 }) // fail

I believe we should not special-case Error, but make this branch work for all objects (expect for arrays/collections of course), regardless of what Object#toString returns.

[marian-r]

@meeber thanks and sorry I haven't seen notifications before. I will try the fix tomorrow.

[marian-r]

@meeber I confirm that the fix for .include() works. Thanks 👍