Fix DeprecationWarnings in tests

The assertRaisesRegexp name was deprecated in Python 3.2 in favor of assertRaisesRegex. Our minimum version requirement is Python 3.5, so this change is fully backwards compatible for our purposes.

The np.all() check would raise a DeprecationWarning if the lengths of the two arrays were not equal. The required additional length check means the early termination moves inside the if-else for iter (i.e. is "t" an np.ndarray or a float). Note that we can skip the length check when "t" is a float, making the early termination a little more generic (also working when len(ts) > 1).