[AIRFLOW-6617] Add tests to PYTHONPATH in breeze

[turbaszek]

Adding tests directory to PYTHONPATH helps during development :)

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Issue link: AIRFLOW-6617

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[potiuk]

Just wondering how it helps ? Not that I am against it but like to see a reason for it and maybe add it for others to the docs how it can be helpful

[turbaszek]

Just wondering how it helps ? Not that I am against it but like to see a reason for it and maybe add it for others to the docs how it can be helpful

It has already happened a few times that I had to set up it manually.

[potiuk]

Yeah. But I wonder when it is needed. I.e. it should not be needed, unless someone (for example) somewhere in our code imports tests not from where it should i.e. import kubernetes instead of import tests.kubernetes -> I'd rather fix those place in the code where those bad imports are used than add tests folder to PYTHONPATH to hide the problem.

[turbaszek]

My problem was not bad imports but running python tests/some/path, mostly used here #6761 to use cli for tests.