Why no __init__.py in tests/unit/**?

[mattpap]

I'm guessing this is intentional. This leads to relative imports like this:

from _util_server import (
    http_get,
    url,
    websocket_open,
    ws_url,
)

which then can't be statically typed (well, at least not straight and would require *.pyi files or moving those utils under bokeh._testing or type checking test files individually).

/cc @bryevdv

[bryevdv]

See the discussion (especially towards the end of the section) here:

https://docs.pytest.org/en/6.2.x/goodpractices.html#tests-outside-application-code

TLDR; it is advised to use "src" directory layout of you add init files. I would like to move to src layout fwiw