assertRaises in unittest not catching Exception properly

You should be passing arguments to the callable separately, as separate arguments:

self.assertRaises(TypeError, add, 1, '1', msg="Additon failed")

Try

def test_additon(self):
    with self.assertRaises(TypeError):
        add(1 + '1')

The problem is that the exception is raised during argument evaluation before self.assertRaises can kick in.