Uses func to compare the expected result with actual result
of a regression test.
diff is ignored.
msg is an optional custom message to print if the
comparison tests positive (i.e. the results differ).
func is the comparison function to use, and must be a
function that returns the same as the built-in cmp().
stackLevel affects exception reporting.
funcArgs is an optional dictionary of keyword arguments that
will be passed to the comparison function, if the dictionary
is not empty.