test(opentelemetry-configuration): simplify management of environment variables

[cjihrig]

Which problem is this PR solving?

The ConfigProvider tests were deleting a number of environment variables after every test, and this logic was duplicated in a few places. This is a bit error prone.

Fixes # N/A

Short description of the changes

The tests seem to pass with a clean process.env provided to each test, and Mocha's afterEach() hook is inherited, so the logic can be simplified a good bit while maintaining semantics.

Type of change

• Bug fix (non-breaking change which fixes an issue) Not really a bug, but more of a simplification.

How Has This Been Tested?

• Existing test suite

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.22%. Comparing base (a26422d) to head (861fe22).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6004   +/-   ##
=======================================
  Coverage   95.22%   95.22%           
=======================================
  Files         311      311           
  Lines        8603     8603           
  Branches     1801     1801           
=======================================
  Hits         8192     8192           
  Misses        411      411           

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[maryliag]

Thanks for the improvement, it's a great idea so we don't forget any variables 😄

I added a suggestion, because we might evolve those tests and need some pre determined variables. This way you save the original values (doesn't need to be inside a before), and restore after every test

[maryliag]

Suggested change

	before(function () {
	process.env = {};
	});
	afterEach(function () {
	process.env = {};
	});
	const _origEnvVariables = process.env
	afterEach(function () {
	process.env = _origEnvVariables;
	});

[cjihrig]

I've made the suggested changes, with a few notes:

1. I had to make copies of process.env, otherwise _origEnvVariables would just be the same object.
2. If the user already has some of these environment variables in their environment, they could potentially interfere with the tests, but it sounds like that is fine.
3. I also fixed up the xxxx placeholders to reference actual pull request numbers.

[otelbot]

Thank you for your contribution @cjihrig! 🎉 We would like to hear from you about your experience contributing to OpenTelemetry by taking a few minutes to fill out this survey.