title: Overriding collection paths via PyTest plugin
body: <p>With PyTest, you can limit the scope of test collection by passing directories/files/nodeids as command line arguments, e.g., <code>pytest tests</code>, <code>pytest tests/my_tests.py</code> and <code>pytest tests/my_tests.py::test_1</code>. Is it possible to override this behavior from within a plugin, i.e., to set them to something else programmatically?</p>
  <p>So far I've attempted setting <code>file_or_dir</code> to my own list within <code>config.option</code> and <code>config.known_args_namespace</code> from the <code>pytest_configure</code> hook, but this appears to have no effect on anything.</p>