Adding operator attribute to assertion error

[rpgeeganage]

This is an attempt to add operator property for the AssertionError.
(As per the issue #1252)
Operators are as follows.

• https://nodejs.org/api/assert.html#assert_assert_deepstrictequal_actual_expected_message
• https://nodejs.org/api/assert.html#assert_assert_notdeepstrictequal_actual_expected_message
• https://nodejs.org/api/assert.html#assert_assert_strictequal_actual_expected_message
• https://nodejs.org/api/assert.html#assert_assert_notstrictequal_actual_expected_message

Please give me feedback on this draft PR.
Thank you.

[codecov]

Codecov Report

Merging #1253 into master will increase coverage by 0.08%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #1253      +/-   ##
=========================================
+ Coverage   94.51%   94.6%   +0.08%     
=========================================
  Files          32      33       +1     
  Lines        1677    1704      +27     
  Branches      405     417      +12     
=========================================
+ Hits         1585    1612      +27     
  Misses         92      92

Impacted Files	Coverage Δ
lib/chai/utils/index.js	100% <100%> (ø)	⬆️
lib/chai/assertion.js	100% <100%> (ø)	⬆️
lib/chai/utils/getOperator.js	100% <100%> (ø)

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[rpgeeganage]

@keithamus ,
Can you please take a peek and give feedback on this when you have time.
(I haven't added any tests yet, I'll add tests when reviewers are fine with the PR).

[keithamus]

The only normative specification of operator is that it is a string right? While I'm fine to default most instances to one of [not][deep][strict]Equal I also think we should provide a mechanism for allowing the operator to be overridden in the assertion.

To me it makes most sense to use flag(this, 'operator') and simply have it default to using getOperator if not present. This way if we find mismatches they're easy to fix by just setting the flag.

That is to say: conceptually this is fine. Let's add flag support, and then that + tests will get a ✅ from me 😄

[rpgeeganage]

@keithamus,
Thanks a lot. I'll do the changes.

[rpgeeganage]

I'm very sorry that,
I have screwed up the branch. so I'm closing this PR and will open a new PR.

[rpgeeganage]

#1257