[FileSystem] Bug: Using IFile.Write... does not update IFileInfo.LastWriteTimeUtc

[pw-sgr]

As the title states using the different write methods of IFile does not change the LastWriteTimeUtc of IFileInfo. Refresh() is called.

In the following example both Console.WriteLine write the same time

Code:

        public static async Task Main(string[] args)
        {
            var fileSystem = new MockFileSystem();
            IFileInfo fileInfo = fileSystem.FileInfo.New("test.txt");
            fileInfo.Create().Dispose();
            fileInfo.Refresh();
            Console.WriteLine(fileInfo.LastWriteTimeUtc);
            await Task.Delay(2000);
            fileSystem.File.WriteAllText(fileInfo.FullName, "test");
            fileInfo.Refresh();
            Console.WriteLine(fileInfo.LastWriteTimeUtc);
        }

Actual Behavior: IFileInfo.LastWriteTimeUtc is not updated after using IFile.Write...

Expected Behavior: IFileInfo.LastWriteTimeUtc is updated to be 2s after the previous read

Possible Solution: It could be related to [FileSystem] Bug: Caching IFileInfo, recreating it, will result in stale cache

[vbreuss]

@pw-sgr : I tried to reproduce this issue and I think the problem is that you use Task.Delay directly. If you replace it with fileSystem.TimeSystem.Task.Delay it works as expected:

	[Fact]
	public async Task Reproduce817()
	{
		var fileSystem = new MockFileSystem();
		IFileInfo fileInfo = fileSystem.FileInfo.New("test.txt");
		fileInfo.Create().Dispose();
		fileInfo.Refresh();
		var previousTime = fileInfo.LastWriteTimeUtc;
		await fileSystem.TimeSystem.Task.Delay(2000); // This line needed to change!
		fileSystem.File.WriteAllText(fileInfo.FullName, "test");
		fileInfo.Refresh();
		var laterTime = fileInfo.LastWriteTimeUtc;
		await That(laterTime).IsOnOrAfter(previousTime.AddSeconds(2.0));
	}

Background information:
The FileSystem uses the mocked TimeSystem for getting the current time. Only when you call Task.Delay on the used time system the mocked current time is updated accordingly.

[pw-sgr]

@vbreuss Seems kinda counterintuitive, as I would've guessed it uses DateTime(Offset).(Utc)Now, when writing, on the other hand it does allow for more precise simulation

[vbreuss]

@pw-sgr:

on the other hand it does allow for more precise simulation

Not only that, but also the delay is simulated, so that the test runs nearly instantaneous although it contains a Task.Delay of 2 seconds.
But I see your point and added the option to replace the used ITimeSystem upon initialization of the MockFileSystem. With the following initialization you can use the real time system:

var fileSystem = new MockFileSystem(o => o.UseTimeSystem(new RealTimeSystem()));

[pw-sgr]

@vbreuss that's neat, I'll still use the mocked time system, as it's faster

[pw-sgr]

Solution: Use IFileSystem.ITimeSystem

Possibility to use the RealTimeSystem was added

Issue resolved