Python unittest - Ran 0 tests in 0.000s

Sidenote: Also, the name of the file in which all the tests are there should start with 'test_'

As stated in the python unittest doc:

The simplest TestCase subclass will simply implement a test method (i.e. a method whose name starts with test)

So you will need to change your method name to something like this:

def test_add_returns_zero_for_emptyString(self):
    self.assertEqual(Add(' '), 0)