The Python documentation states that the -t option controls the:
Top level directory of project (defaults to start directory)
Usually people use the -s option (python -m unittest discover tests/ is equivalent to python -m unittest discover -s tests), and I have never seen anyone use -t before. The brief description in the documentation is not enlightening to me.
What does the "top level directory" mean in this particular context? What exactly does the -t option do?
My understanding is that although the top-level directory defaults to whatever the starting directory is, the starting directory must be contained by the test directory.
From the first paragraph on test discovery:
Unittest supports simple test discovery. In order to be compatible with test discovery, all of the test files must be modules or packages (including namespace packages) importable from the top-level directory of the project (this means that their filenames must be valid identifiers).
Suppose you have a directory structure like
./
tests1/
tests2/
If ./ is the top-level directory and tests1 is the starting directory, no tests will discovered under tests2, even though tests2 is importable from the top-level directory.
The purpose of -s would be to discover only a subset of tests for a particular project. The purpose of -t might be to choose a particular "subproject" to run tests for.