Unclosed file descriptors in tests

[DPeled]

Hey everyone!

As I reviewing the code as part of PR I'm working on, I found lines in the pytest tests that using the open() function without a with, and the file never closed.

Example for such line: https://github.com/pytorch/serve/blob/873edc50cc6059c47830a5d30bbbdbe1e1a3d9bb/test/pytest/test_handler.py#L41

[DPeled]

I fixed it in my PR, this issue is on me