With sleep(0.2) a multiple of sleep(0.1), the order of task 2 and 3
execution is not well defined, and depends on the precision of the system
clock and how fast the rest of the code runs. So change 0.2 to 0.18 to
make the test more reliable.
Also fix a typo of t3/t4, and cancel t4 at the end.
Signed-off-by: Damien George <damien@micropython.org>
Otherwise a task that continuously awaits on a large negative sleep can
monopolise the scheduler (because its wake time is always less than
everything else in the pairing heap).
Signed-off-by: Damien George <damien@micropython.org>