Test sometimes fails on AppVeyor (Windows). 300/50=6, but there could be
environment factors that miss the timer interval on the "edges".
timer_start() does not have such a hard requirement.
this is consistent with vim, and is necessary for plugins that implement
their own input modes using "getchar()" and still want to do async
event processing.
It is otherwise impossible to determine which test failed sanitizer/valgrind
check. test/functional/helpers.lua module return was changed so that tests which
do not provide after_each function to get new check will automatically fail.