fix: cpu count bug, lack of lockfile and add missing tests

[phawxby]

What is the purpose of this pull request?

Ultimately this started as a PR to fix a bug I was seeing when mocking os with jest, it grew a little bit when I found other issues.

What changes did you make? (Give an overview)

• Fixing a bug which presentes with jest mocking os
• Adding tests for the above as well as the cpus() = [] edge case
• Add an npm lockfile because simply using npm install does not result in a working repo because the wrong versions of various modules are installed. I had step backwards through module versions until I found versions that worked. I don't know why these were excluded.

It is highly recommended you commit the generated package lock to source control: this will allow anyone else on your team, your deployments, your CI/continuous integration, and anyone else who runs npm install in your package source to get the exact same dependency tree that you were developing on.