MockFileSystem sets current directory to actual FS

[dzarda]

It appears that the MockFileSystem constructor calls real filesystem API when the currentDirectory parameter is left empty.

The current directory is then set as C:\Users\...\AppData\Local\Temp

I suspect the following code

    public MockFileSystem(IDictionary<string, MockFileData> files, string currentDirectory = "")
    {
        if (string.IsNullOrEmpty(currentDirectory))
        {
            currentDirectory = IO.Path.GetTempPath();
        }
        ...

in https://github.com/System-IO-Abstractions/System.IO.Abstractions/blob/4b8ff76fb410e15d26ab2cab807117323de08299/System.IO.Abstractions.TestingHelpers/MockFileSystem.cs#L22

[fgreinacher]

Thanks for reporting this! I see a few options here:

• Not setting the current directory unless explicitly specified. Unsure what would be the effect of this though.
• Setting it to some hardcoded path, e.g. c:\temp. Should be safe and is predictable.
• Leaving it as is. I don't see too big a problem with the current approach as getting the temp path is non-invasive.

Thoughts?

[josteink]

Setting it to some hardcoded path, e.g. c:\temp. Should be safe and is predictable.

That's a very Windows-centric point of view :)

[ewlloyd]

After a quick glance, I think that not setting it at all would cause issues in the MockDirectory.EnsureAbsolutePath() method (used by MockDirectory.GetFiles() and MockDirectory.EnumerateDirectories()).

The only question I'd have with leaving it as is, is whether there'd ever be a case where you wouldn't have the real IO.Path available.

[dzarda]

I feel having a safe default is desired. Why can't we use the "root" concept for this; "C:" and "/" respectively?

I think the current behavior is unwanted. Reason why this issue exists is because I spent an hour figuring out the unexpected behavior.

[ewlloyd]

Fair enough. What was expected behavior, in your case?

[dzarda]

The struggle boiled down to something along the lines...

var fs = new MockFileSystem();
var dirInfo = fs.DirectoryInfo.FromDirectoryName("."); // System.IO.DirectoryNotFoundException : Could not find a part of the path 'C:\Users\....\AppData\Local\Temp

In such case I'd like fs to have an empty filesystem present, with only the root directory. Having CD pointing here as well makes perfect sense to me.