comment fix
test fix - thanks @cyli

The release call has not been called yet. There should be only 7
calls (write, read, 5 writes), whereas this call only gets the first 4
writes. Hence, checking last 5 writes.
not releasing after test

It'll not have dirty reactor since clock is not a real reactor. Also,
improved another test regarding the same
updated docstring with new heart beat strategy - per @dreid