Asserting on callCount with a numeric string results in very confusing failure message

[cincodenada]

Describe the bug
This bug was originally reported in sinon-chai by @BebeSparkelSparkel as chaijs/sinon-chai#136 but turned out to be an issue with Sinon itself. The bug is that we can get the error message AssertError: expected spy to be called 10 times but was called 10 times - this happens when specifying callCount as a string.

To Reproduce
I made a slightly modified version of the original test case so that it just uses Sinon:

const sinon = require('sinon');
const n = '10',
      s = sinon.spy();
for(let i=0; i < n; ++i) s();

sinon.assert.callCount(s, n);

Run the above, you will get AssertError: expected spy to be called 10 times but was called 10 times which is a very confusing error message.

Expected behavior

One of two options:

1. Sinon could coerce numeric strings into numbers, and pass the assertion
2. Sinon could surface the actual problem, which is that callCount was not a number.

Both of these seem sensible, the first is a little more user-friendly, the second is a little more correct.

Internally it looks like Sinon raises a TypeError, which is I think what is actually triggering this failure, so it could just surface that, or it could attempt to convert to a number.

This actually happens with any string: sinon.assert.callCount(s, 'banana') will get you expected spy to be called banana times but was called 10 times, which is less confusing, but also it would probably be better to instead fail with an error about banana not being a number.

Context (please complete the following information):

• Library version: All versions (tested with most recent releases for v1-11, including 11.1.2)
• Environment: OS X
• Other libraries you are using: None

[fatso83]

Great bug report. We always lean on the side of being correct and throwing early rather than try and coerce types, so any fix should take that into account.