Improve testing coverage - cov-fail-under setting

[briangrossman]

As an xPRO engineer, I want to ensure I have proper test coverage on all the code. As referenced in #2076, we should add the flag --cov-fail-under=NN for our baseline coverage percentage, increasing it as we work our way to 100% coverage. Start at 85%.

Designs and Mockups

Peter discovered this doc, which should be helpful.

Acceptance Criteria:

• Configure the option --cov-fail-under=NN

[HamzaIbnFarooq]

@briangrossman is adding more tests under the scope of this PR? as if we use the mentioned code coverage threshold 85 it will start failing all the new PRs because the current code coverage is 82.74.

For now, I have added 82.70 as the threshold value, so new PRs will not be blocked until they decrease the Performace to 82.70.

[rhysyngsun]

@HamzaIbnFarooq increasing test coverage is scoped in #2076

[briangrossman]

@HamzaIbnFarooq : Good point about the threshold. Setting it to 82.70 is perfect. Thanks for adding the list to #2076, too!