fix: Ensure drain target is a valid event emitter before subscribing

[metal-messiah]

Ensure that the drain target is a valid event emitter to ensure that the .on method exists and will not throw errors.

Overview

Related Issue(s)

https://newrelic.slack.com/archives/C0193KAHHAS/p1724879485394419

Testing

New unit test has been added to validate the behavior

[github-actions]

Asset Size Report

Merging this pull request will result in the following asset size changes:

Agent	Asset	Previous Size	New Size	Diff
lite	loader	32.66 kB / 11.35 kB (gzip)	32.71 kB / 11.37 kB (gzip)	0.16% / 0.16% (gzip)
lite	async-chunk	50.83 kB / 16.35 kB (gzip)	50.83 kB / 16.35 kB (gzip)	0% / 0% (gzip)
pro	loader	53.86 kB / 18.05 kB (gzip)	53.91 kB / 18.07 kB (gzip)	0.09% / 0.07% (gzip)
pro	async-chunk	99.3 kB / 29.69 kB (gzip)	99.3 kB / 29.69 kB (gzip)	0% / 0% (gzip)
spa	loader	61.79 kB / 20.5 kB (gzip)	61.84 kB / 20.51 kB (gzip)	0.08% / 0.07% (gzip)
spa	async-chunk	114.44 kB / 34.03 kB (gzip)	114.44 kB / 34.03 kB (gzip)	0% / 0% (gzip)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.70%. Comparing base (84bd299) to head (b298dcb).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1167      +/-   ##
==========================================
- Coverage   88.82%   88.70%   -0.12%     
==========================================
  Files         161      161              
  Lines        7357     7359       +2     
  Branches     1457     1459       +2     
==========================================
- Hits         6535     6528       -7     
- Misses        704      712       +8     
- Partials      118      119       +1     

Flag	Coverage Δ
integration-tests	91.78% <100.00%> (-0.26%)	⬇️
unit-tests	78.76% <100.00%> (ø)

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[github-actions]

Last ran on August 29, 2024 09:55:52 CDT
Checking merge of (b298dcb) into main (84bd299)