This adds the Python files in the tests/ directory to be formatted with
./tools/codeformat.py. The basics/ subdirectory is excluded for now so we
aren't changing too much at once.
In a few places `# fmt: off`/`# fmt: on` was used where the code had
special formatting for readability or where the test was actually testing
the specific formatting.
CPython does not have an implementation of select.poll() on some
operating systems (Windows, OSX depending on version) so skip the
test in those cases instead of failing it.
This test doesn't check the actual I/O behavior, just "static" invariants
like behavior on duplicate calls or calls when I/O object is not registered
with poller.
