'Test sign for a given interface.'

def sign_for_intf(self, interface):

    mat = interface.const_to_matrix([[1, 2, 3, 4], [3, 4, 5, 6]])
    self.assertEqual(intf.sign(mat), (True, False))
    self.assertEqual(intf.sign((- mat)), (False, True))
    self.assertEqual(intf.sign((0 * mat)), (True, True))
    mat = interface.const_to_matrix([[(-1), 2, 3, 4], [3, 4, 5, 6]])
    self.assertEqual(intf.sign(mat), (False, False))
