Request: Add notes about where to put unit tests

I did some Googling. None of the pages have very good explanations of where to put your unit test files.

Also, AFAIK (I am a Python newbiew) there are some drawbacks to <project_root>/test/ about importing. Might need to modify PYTHONPATH during unit test runs.

Also, please talk about why init.py is important for unit tests. A few places recommend it... but I thought it was dead in Python3.

Ref: http://pytest.org/latest/goodpractises.html
Ref: http://stackoverflow.com/questions/5341006/where-should-i-put-tests-when-packaging-python-modules
Ref: http://stackoverflow.com/questions/61151/where-do-the-python-unit-tests-go

未指定目標檔案或測試。先查看連結的 pytest 最佳實務與封裝相關討論，然後找到相關的測試文件。完成的標準是說明測試檔案的放置位置、import/PYTHONPATH 方面的考量，以及 init.py 在 Python 3 中的作用。