Potential bug in FakeTime.restoreFor

[meooow25]

It is possible for previously queued code to execute between the restore and override steps in restoreFor, which means they unexpectedly use the native time functions.

mock/time.ts

Lines 337 to 342 in cf21e99

	time.restoreGlobals();
	try {
	result = await callback.apply(null, args);
	} finally {
	time.overrideGlobals();
	}

I found this when using delay (which in turn uses restoreFor).

import { FakeTime, NativeTime, delay } from "https://deno.land/x/mock@v0.9.4/time.ts";

function isNative(prefix) {
  console.log(prefix, setTimeout === NativeTime.setTimeout ? "native" : "not native");
}

async function fun() {
  await Promise.resolve();
  // I expect setTimeout to be fake here but it is not
  isNative("fun");
}

const ft = new FakeTime();
isNative("before");
fun();
await delay(0);
isNative("after");

// outputs:
// before not native
// fun native
// after not native

[KyleJune]

fun is asynchronous. Without awaiting it before calling the delay function that restores native time, there is a chance that native time would be restored temporarily while the code in fun is running. You could encounter a similar issue if you were to call ft.restore() after fun without awaiting it.

[meooow25]

I realize how it works, but my intent was to point out that someone using the library may not immediately figure out that delay/restoreFor has such a side effect. Whether this needs a fix, the choice is yours.