Instead of using a feature check. This is more consistent with how other
optional modules are skipped.
Signed-off-by: Damien George <damien@micropython.org>
Previously, there was no test coverage of the "write failed" path. In
fact, the assertion would fire instead of gracefully raising a Python
exception.
Slightly re-organize the code to place the assertion later. Add a test
case which exercises all paths, and update the expected output.
Signed-off-by: Jeff Epler <jepler@gmail.com>
