The pytest-xdist plugin extends py.test with some unique test execution
modes:

Test run parallelization: if you have multiple CPUs or hosts you can use
those for a combined test run. This allows to speed up development or to
use special resources of remote machines.

--boxed: run each test in a boxed subprocess to survive SEGFAULTS or
otherwise dying processes

--looponfail: run your tests repeatedly in a subprocess. After each run
py.test waits until a file in your project changes and then re-runs the
previously failing tests. This is repeated until all tests pass after
which again a full run is performed.

Multi-Platform coverage: you can specify different Python interpreters
or different platforms and run tests in parallel on all of them.
