You could use `test` instead of `test.pytest` above; Pants then applies the
passthrough args to tools called by all of `test`, not just `test.pytest`.
This gets tricky. We happen to know we can pass `-k list` here, that `pytest` accepts passthrough
args, and that this `test` invocation upon `tests/python/...` won't invoke any other tools
(assuming nobody hid a `junit` test in the `python` directory).

Append arguments that append to a list can be specified more than one time.  When specifying more
than one test to run at a time, you could run:

     ./pants test.junit --test="MyMainTest" --test="MySideTest" ./coolbeans::