instanceof checks may not be sufficient in node

[tandrewnichols]

This is sort of an edge case, so I'd understand if you didn't want to bother with it. I just added this package to our jasmine suite, and .toBeFunction() is reporting "Expected Function to be function." The reason is that we are using sandboxed-module, which loads the subject under test using the vm module (in a separate context). instanceof doesn't seem to work when comparing objects from different contexts. E.g. (in our case):

// vm context - i.e. the subject-under-test
exports.a = function() {}

// test
expect(obj.a).toBeFunction() // fails because obj.a instanceof Function is false

For what's it worth, I don't blame you for this. The vm context instanceof problem is super annoying, and I've run into it before too. You might be able to do other checks in addition to instanceof to cover such cases. Something like return this.actual isntanceof Function || typeof this.actual === 'function' || this.actual.apply.

[JamieMason]

Very interesting, thanks for this. I see no harm in hardening the checks to cover this. Thank you.

[tandrewnichols]

Also for what it's worth, it looks like these are known issues in sandboxed-module that they are trying to fix. See felixge/node-sandboxed-module#44 and felixge/node-sandboxed-module#13.

[JamieMason]

I think just return typeof this.actual === 'function'; should be enough to cover this, do you agree or is more needed @tandrewnichols?

[tandrewnichols]

Yeah, I imagine that would be enough.