For the caller there should be no difference if there is no message
in the queue and if there can't be a message in the queue.
The current API works as one would expect if there is a message queue,
but once called from a thread that does not have a message queue
configured, code that does
while (msg_avail())
will end up in an infinite loop.
Remove this foot-gun from the API by making the return value of
msg_avail() independend of the availability of a message queue.
- Define test_utils_interactive_sync as DEFAULT_MODULE in Makefile.tests_common
- For tests disabling autoinit, add test_utils_interactive_sync to main
- Add DISABLE_MODULE += test_utils_interactive_sync for tests requiring
sudo, `tests/shell`, `tests/minimal` and `tests/stdin`
- Add shell_commands to tests/periph_wdt and tests/struct_tm_utility to
pull `r` and `s` commands
- Remove includes and usage in `tests/main.c` for tests that where
already using test_utils_interactive_sync
