Code coverage needs some help

[jdmarshall]

I've added some tests to the new functionality in worker.js and cluster.js but for the most part the same code that had no coverage in cluster.js now has no coverage in worker.js

metrics.js is also low, particularly for branches.

I don't think we need CHANGELOG entries for this work so I'll be ignoring PR errors related to omitting them.

[WilliamK112]

I’d like to take a focused part of this now that the 0.16.0 changes are on main: add direct coverage for the shared lib/metric.js constructor contract (non-object config, missing help/name, invalid collect, and valid defaults/label ordering). I’ll keep it separate from the worker.js work in #816 and won’t close this broader coverage issue.

[tahakotil]

I would like to take a non-overlapping slice: direct tests for the failure fallbacks in lib/metrics/helpers/safeMemoryUsage.js and safeRss.js. I will keep this separate from the claimed metric.js scope and worker.js work, and will reference rather than close this broader coverage issue.

[jdmarshall]

Two PRs have been a good improvement. Not stopping anyone else from offering more but I think this'll do for now, especially once some deprecated functions get deleted.