Just to be clear, the current implementation is limited to substring matches. It doesn't support py.test like "and/or" combinators. (Actually, py.test uses 'eval' to support arbitrary patterns.)

So say we have test case

SomeClass
    test_foo
    test_bar

Then

- python -m unittest -k fo matches "test_foo"
- python -m unittest -k Some matches "test_foo" and "test_bar"
- python -m unittest -k some matches nothing

The -k option may be used multiple times, combining the patterns with "or":

- python -m unittest -k fo -k b matches "test_foo" and "test_bar"

It's also possible to use glob-style patterns, like -k "spam_*_eggs".