All required file system features should ideally be extracted into a separate interface and tests should work with its mock. At the very least, though, the test should use a directory path that's guaranteed to be empty/non-existing, such as a random + verified path in user's %TEMP%.
The test AbsolutePathShouldNotChange in https://github.com/sukona/Grapevine/blob/master/src/Grapevine.Tests/Server/PublicFolderFacts.cs#L38 should not be relying on existence/contents of actual filesystem directory "C:\temp".
All required file system features should ideally be extracted into a separate interface and tests should work with its mock. At the very least, though, the test should use a directory path that's guaranteed to be empty/non-existing, such as a random + verified path in user's %TEMP%.