Maintenance: metrics unit testing strategy

[alan-churley]

Description of the feature request

Problem statement
Metrics unit tests currently are not structured the same as the Logger module,

In the logger only public methods are tested, following the recommendations here: https://github.com/goldbergyoni/javascript-testing-best-practices/#-%EF%B8%8F-14-stick-to-black-box-testing-test-only-public-methods

Opening a ticket to track discussions and work on improving this,

Related issues, RFCs

#102

[dreamorosi]

The issue is still current so contributions are welcome.

This is a good issue for newcomers as it allows to understand how the utility works in depth, as well as for those who are looking at sharpening their Jest skills.

If anyone is interested in picking this up, please leave a comment here, then discuss your findings / proposed changes before opening a PR.