removed extra cruft from debug_check_board

I had a few simple manual tests in addition to the full line of
tests for debug check board. That's unecessary, since I'm testing
for every possible value in a 3x3 array at the moment
added test for count_zeros function
added check_for_assertion_error to test function

check_for_assertion_error takes a function and a list of arguments,
applies the list of arguments to the function, and checks to see
if an assertion is raised
added test for swap_players