Mock filesystem in integration testing

Question

I'm writing a ruby program that executes some external command-line utilities. How could I mock the filesystem from my rspec tests so that I could easily setup some file hierarchy and verify it after testing. It would also be best to be implemented in ram so that tests would run quickly.

I realize that I may not find a portable solution as my external utilities are native programs interacting directly with operating system file services. Linux is my primary platform and solution for that would suffice.

Answer 1

Maybe this won't answer your question directly, but in such cases I tend to create a temporary directory during test setup and remove it on teardown. Of course you also have to ensure the application writes to this temporary directory. I always have a configuration option defining destination directory that I can overwrite during testing.

When it comes to assertions I use plain File.exist? or File.directory?, but of course you can create your own wrappers around it. If you need some initial state you can build a directory that can be used as a fixture and will be copied to the temporary direcory during test setup.

Answer 2

You can create a big file (size of you dummy disk) and mount the file as a loop-back device. You can create any filesystem and directory structure on this device.
You can create 2 of them and make even simple diff compare to ensure data integrity after tests.
I hope i understand you requirements correctly since i don't sure why simple ramdisk solution is not good enough.
This might be relevant as well.

Answer 3

Have you checked out FakeFS or MockFS?