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pythondebuggingmonkeypatching

mocking os.path.exists without affecting debugger

I am writing a unittest for a python script which does heavy file operations via os and hence I mocked some of the os functions. I noticed a strange behavior when patching the return value of os.path to return False via:

@pytest.fixture(autouse=True)
def init_mocks(monkeypatch):
    monkeypatch.setattr(
        mymodule.os.path, "exists", Mock(return_value=False))

My debugger (within VSCode) does not work at all or behaves really strange. Is there a way to mock os.path without affecting the debugger?

Solution

  • After some research I now understand, that monkeypatching affects the whole python runtime - and hence potentially also the debugger. (I found effects with os.path.exists as well as with os.path.join)

    So, to patch os.path.exists while still being able to debug, I instead patched it via context manager:

    @pytest.fixture(autouse=True)
def mock_os_path_exists():
    with patch('hdbPackageComposer.os.path.exists', Mock(return_value=True)):
        yield