"atexit" module: PyFakeFS not active anymore at application exit

[buhtz]

Hello,
I am assuming there is no nice solution it despite of mocking and tricking around. But I just want to ask and report my observations.

I have a class StateData representating a state file (like a config file) on disc. It's save() method write the data to disc. That method is triggered at application exit using atexit.register().

In unit tests I use PyFakeFS to prevent writing to real disc. I observed that PyFakeFS seems not to be "active" anymore when atexit does its job on application exit. The file was written to real disc.

For technical details see my PR bit-team/backintime#2003 "fixing" the problem just with removing the relevant unit tests.

Of course I can mock around. But I don't want that. Might I forget any other elegant solution?

[mrbean-bremen]

Out of the box I don't have a solution for this, and it is certainly not possible with the current pyfakefs usage. pyfakefs has to make sure that the filesystem functions are restored after the test ends, and this is certainly before the atexit hook is triggered. Just not resetting the filesystem would most probably have other unwanted side effects.

You could test this by patching/overwriting Patcher.tearDown to do nothing and check how that will behave, though that would also mean that you have to make sure to run this test separately. Generally, I don't think that this is a good idea.