The -s option shown in `python3 -m unittest -h` is grouped under help for discover. Options for a discover command don't necessarily apply to the unittest command itself.

$ python3 -m unittest -h
usage: python3 -m unittest [-h] [-v] [-q] [--locals] [-f] [-c] [-b]
                           [-k TESTNAMEPATTERNS]
                           [tests [tests ...]]

positional arguments:
  tests                a list of any number of test modules, classes and test
                       methods.

optional arguments:
  -h, --help           show this help message and exit
  -v, --verbose        Verbose output
  -q, --quiet          Quiet output
  --locals             Show local variables in tracebacks
  -f, --failfast       Stop on first fail or error
  -c, --catch          Catch Ctrl-C and display results so far
  -b, --buffer         Buffer stdout and stderr during tests
  -k TESTNAMEPATTERNS  Only run tests which match the given substring

Examples:
  python3 -m unittest test_module               - run tests from test_module
  python3 -m unittest module.TestClass          - run tests from module.TestClass
  python3 -m unittest module.Class.test_method  - run specified test method
  python3 -m unittest path/to/test_file.py      - run tests from test_file.py

usage: python3 -m unittest discover [-h] [-v] [-q] [--locals] [-f] [-c] [-b]
                                    [-k TESTNAMEPATTERNS] [-s START]
                                    [-p PATTERN] [-t TOP]

optional arguments:
  -h, --help            show this help message and exit
  -v, --verbose         Verbose output
  -q, --quiet           Quiet output
  --locals              Show local variables in tracebacks
  -f, --failfast        Stop on first fail or error
  -c, --catch           Catch Ctrl-C and display results so far
  -b, --buffer          Buffer stdout and stderr during tests
  -k TESTNAMEPATTERNS   Only run tests which match the given substring
  -s START, --start-directory START
                        Directory to start discovery ('.' default)
  -p PATTERN, --pattern PATTERN
                        Pattern to match tests ('test*.py' default)
  -t TOP, --top-level-directory TOP
                        Top level directory of project (defaults to start
                        directory)

For test discovery all test modules must be importable from the top level
directory of the project.