ImageProcessor FileDependency breaks object deletion in unit tests

[Lartza]

With a very simple FileDependency model and unit test, deleting rows causes a PermissionError: [WinError 32] The process cannot access the file because it is being used by another process: 'C:\\Users\\lartz\\PycharmProjects\\djangoProject\\images\\image_UQbw8fZ.jpg' error.

Minimal code and traceback:
https://gist.github.com/Lartza/84c69826b3f9eb238acf994806f6738c

EDIT: In a bigger project where I discovered this, removing images is possible from the Django Rest Framework API root

[Lartza]

Closing the image field with

i = Image.objects.create(image=data)
i.image.close()

or running gc.collect() after create seems to let the following .get().delete() work correctly

[lehins]

Interesting issue. Unfortunately I don't have any bandwidth to investigate it. Moreover, I haven't used this library or even python for that matter for over 5 years. @Lartza would you like to submit a PR with a fix and a test case for this, cause it doesn't look like I will get to it anytime soon?

[Lartza]

It's certainly something I'm willing to investigate more when I have some time, even if I'm not sure I have the skills required to fix it.

It was suggested on IRC this would be much less likely to happen running under Linux and that requires some investigation to confirm, but for now if the issue doesn't happen in production I can likely work around it in testing and can't spend time on this for a few weeks now due to deadlines.