The pytest-xdist plugin extends py.test with some unique test execution modes. Multiple CPUs/hosts can be used for a combined test run. Each test can be run in a boxed subprocess (not win) to survive SEGFAULTS or otherwise dying processes. Tests can be run in loop on failure; the plugin waits for file changes and then re-runs failing tests. The plugin also provides multi-platform coverage by allowing the developer to specify different Python interpreters or different platforms.