<s>[INST] Where do the Python unit tests go? If you're writing a library, or an app, where do the unit test files go?  
It's nice to separate the test files from the main app code, but it's awkward to put them into a "tests" subdirectory inside of the app root directory, because it makes it harder to import the modules that you'll be testing.  
Is there a best practice here?
 [/INST] For a file module.py, the unit test should normally be called test_module.py, following Pythonic naming conventions.
There are several commonly accepted places to put test_module.py:

In the same directory as module.py.
In ../tests/test_module.py (at the same level as the code directory).
In tests/test_module.py (one level under the code directory).

I prefer #1 for its simplicity of finding the tests and importing them. Whatever build system you're using can easily be configured to run files starting with test_. Actually, the default unittest pattern used for test discovery is test*.py.
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