fix: begin running tests immediately instead of waiting for watcher

[jedwards1211]

PR Checklist

• Addresses an existing open issue: fixes 🚀 Feature [watch mode]: begin running tests immediately instead of waiting for watcher ready event #5372
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Turn off ignoreInitial and distinguish between initial 'add' events and paths added after test startup. We can compare the mtime of the path to the test startup time to decide if the change should trigger a rerun.

[jedwards1211]

@mark-wiemer is using new Date() allowed in the CLI code? An ESLint rule complains about it. If not is there any way I can get the current time to compare to file timestamps?

Also, let me know if you have any opinions about if/how I should test this change. It would be nice if I could inject some kind of chokidar mock so I can control timing of the file events to be able to verify in a test that it runs before the ready event is emitted...but the only easy way I think of to do that would be to call things in watch-run.js directly from the test process instead of executing mocha --watch in a separate process.

[mark-wiemer]

The earlier versions of Mocha using Chokidar 3 still waited until watcher.on('ready') to call mocha.runGlobalSetup(), but I'm not sure why. A quick look at the code isn't too revealing, but I see why we'd want to call this right away. I'm curious if we can add a test case that has a complex global setup to ensure things still work?

[jedwards1211]

I'm not exactly familiar with what that global setup is (loading required modules?) but I can try to figure out what goes into it

[jedwards1211]

Okay Chokidar doesn't seem to specify whether 'change'/'unlink' events can get emitted before 'ready' if changes occur during its initial scan, but if so, it could cause the preexisting code here to start running tests before it's performed global setup.

Obviously the intention of the preexisting code is to wait for the 'ready' event to run everything for the first time (first global setup, then the first test run).

I've fixed this in my PR now, if it gets an event before the global fixture context has been created it won't schedule a rerun.

(I still need to write tests for this)

[mark-wiemer]

Marking as draft until tests are added