Fix usage of this.skip() within tests

[rsimha]

Using this.skip() within tests can cause afterEach() to be skipped. mochajs/mocha#2148

In addition, this.skip() doesn't work from within a nested describe block. mochajs/mocha#2683

Figure out how to get past these two issues while still allowing tests to dynamically skip themselves.

[rsimha]

/cc @jridgewell @choumx @cramforce @lannka @aghassemi @alanorozco

From the debugging I did, this.skip() is causing dirty global state in a handful of test suites, which could explain a chunk of the seemingly arbitrary failures we've been seeing.

Sadly, I don't think there's a good workaround at the mocha level to get past this. We're going to have to come up with a way to not call this.skip() if a test must be skipped, but instead make the test return without doing anything.

[rsimha]

According to https://mochajs.org/#inclusive-tests, use of this.skip() is okay in before(), since none of the beforeEach() setup is done at that point. The problem only occurs when this.skip() is called in beforeEach(), because by then, the global beforeEach() will have been run, but the global afterEach() will be bypassed.

I think we can work with this limitation.

In addition, there's a workaround for using this.skip() in a nested describe block that we should put in place: mochajs/mocha#2683 (comment)