==================
- Avoid hardcoding ``sys.argv[0]`` as script;
allow, for instance, Zope 2's `bin/instance test` (LP407916).
- Produce a clear error message when a subprocess doesn't follow the
``zope.testing.testrunner`` protocol (LP407916).
- Avoid unnecessarily squelching verbose output in a subprocess when there are
not multiple subprocesses.
- Avoid unnecessarily batching subprocess output, which can stymie automated
and human processes for identifying hung tests.
- Include incremental output when there are multiple subprocesses and a
verbosity of ``-vv`` or greater is requested. This again is not batched,
supporting automated processes and humans looking for hung tests.