test: MemoryTests/AbsoluteExpirationRelativeToNowExpiresCorrectlyAsync is flaky

[kiminuo]

From time to time, AbsoluteExpirationRelativeToNowExpiresCorrectlyAsync https://github.com/zkSNACKs/WalletWasabi/pull/6159/checks?check_run_id=3288453648 fails. I have tried to make it fail on Windows 10 and I couldn't. I tried on Linux and it seems it fails there much more often (like 1 / 1000 attempts or so).

I believe we hit dotnet/runtime#45585 issue here:

[Fact]
public async Task AbsoluteExpirationRelativeToNowExpiresCorrectlyAsync()
{
	// This should be buggy but it seems to work for us: https://github.com/alastairtree/LazyCache/issues/84
	using var cache = new MemoryCache(new MemoryCacheOptions());

	var result = await cache.AtomicGetOrCreateAsync(
		"key",
		new MemoryCacheEntryOptions { AbsoluteExpirationRelativeToNow = TimeSpan.FromMilliseconds(20) },
		() => Task.FromResult("foo"));
	Assert.Equal("foo", result);

	result = await cache.AtomicGetOrCreateAsync(
		"key",
		new MemoryCacheEntryOptions { AbsoluteExpirationRelativeToNow = TimeSpan.FromMilliseconds(20) },
		() => Task.FromResult("bar"));
	Assert.Equal("foo", result);

	await Task.Delay(TimeSpan.FromMilliseconds(21)); // <-- XXX: THIS CAN TAKE LESS THAN 21 milliseconds

	result = await cache.AtomicGetOrCreateAsync(
		"key",
		new MemoryCacheEntryOptions { AbsoluteExpirationRelativeToNow = TimeSpan.FromMilliseconds(20) },
		() => Task.FromResult("bar"));
	Assert.Equal("bar", result);
}

on my linux machine I get rarely 19 milliseconds instead of 21 on line XXX when measuring with Stopwatch and in that case the test fails.

I believe it would be better to use Thread.Sleep(21) instead of await Task.Delay(TimeSpan.FromMilliseconds(21)) here. So far with this change, it did not fail for me. So it may not fix the issue entirely but it may make it better.

@nopara73 @molnard @lontivero WDYT?

[nopara73]

Go ahead