Add more tests for v flag

[tannal]

Fix #4077

[ptomato]

Thanks!

For full testing of the v flag it'd be good to make sure that all of the basic tests of the u flag are also carried out for v. But it's fine not to consider that in the scope of this PR.

[ptomato]

I would suggest using assert.compareArray for these, it's more precise and you'll get better error messages if the test fails.

Suggested change

	assert.sameValue(doExec(/𠮷/).toString(), "𠮷,0", "Basic exec without v flag");
	assert.compareArray(doExec(/𠮷/).toString(), ["𠮷", 0], "Basic exec without v flag");

(etc.)

Same suggestion for elsewhere throughout the PR.

You'll need to add includes: [compareArray.js] to the front matter for that to work.

[tannal]

The assert.compareArray only works for one-dimensional arrays. For the matchAll test, should I just keep my original string comparison?

[ptomato]

Not ideal (especially the last assertion with empty matches is kind of confusing), but if you want to leave it as is I'm OK with it.

flatMap would be nicest, but I'd prefer not to fail the test on engines that haven't implemented flatMap yet. So that's out.

One possibility could be to do something like this:

function doMatchAll(regex) {
  const result = RegExp.prototype[Symbol.matchAll].call(regex, text);
  const matches = Array.from(result, m => m[0]);
  const indices = Array.from(result, m => m.index);
  return matches.concat(indices);
}

// ...

assert.compareArray(
  doMatchAll(/𠮷/g),
  ["𠮷", "𠮷", "𠮷", 0, 3, 6],
  "Basic matchAll with g flag"
);

// ...

assert.compareArray(
  doMatchAll(/(?:)/gv),
  ["", "", "", "", "", "", 0, 2, 3, 5, 6, 8],
  "Empty matches with v flag"
);

[tannal]

Good idea. I can try this in the follow-up PR. BTW, thanks for the feedback, which is very helpful.

[tannal]

For full testing of the v flag it'd be good to make sure that all of the basic tests of the u flag are also carried out for v.

I can open a follow up PR later on for this part.