fix: enhance test on pr 583

[gnought]

In PR #583, the fix is valid but the unit test does not. The test is still pass when we revert the line back to

packet.writeCallback = next

The PR mentioned Aedes uses through2 and suffers similar bugs. The claim is partially correct. We need to do a fix but it is due to the nodejs Transform callback behaviour, in our case it is writeCallback call. We could refer to nodejs doc https://nodejs.org/docs/latest-v16.x/api/stream.html#transform_transformchunk-encoding-callback

The callback function must be called only when the current chunk is completely consumed. The first argument passed to the callback must be an Error object if an error occurred while processing the input or null otherwise. If a second argument is passed to the callback, it will be forwarded on to the transform.push() method.

This PR is to fix the unit test on PR #583.

[coveralls]

Pull Request Test Coverage Report for Build 1800150339

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.911%

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Totals
Change from base Build 1799508029:	0.0%
Covered Lines:	800
Relevant Lines:	800

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 1800150339

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.911%

---

Totals
Change from base Build 1799508029:	0.0%
Covered Lines:	800
Relevant Lines:	800

---

💛 - Coveralls

[robertsLando]

. We need to do a fix but it is due to the nodejs Transform callback behaviour, in our case it is writeCallback call. We could refer to nodejs doc

What could be a fix to this?

[gnought]

The fix in #583 is fine, not to pass 2nd argument to in the Transform callback. :)