Testing with the file system

I've come across the following solutions to writing tests which require access to the file system:

• Write Integration tests, not unit tests. For this to work you need a simple way of creating a folder where you can dump stuff without worrying about other tests interfering. I have a simple TestFolder class which can create a unique per test method folder to use.

• Write a mockable System.IO.File. That is create a IFile.cs. I find using this often ends up with tests that simply prove you can write mocking statements, but do use it when the IO usage is small.

• Examine you layer of abstraction, and extract the file IO from the class. The create a interface for this. The remainder use integration tests (but this will be very small). This differs from above in that instead of doing file.Read you write the intent, say ioThingie.loadSettings()

• System.IO.Abstractions. I've not used this yet, but it is the one I'm most excited about playing with.

I end up using all the methods above, depending on what I'm writing. But most of the time I end up thinking abstraction is wrong when I write unit tests that hit the IO.

Edit:  2013-05-21: Moved code to Git Gist.