import unittest

# Assuming your function is imported or defined here:
# from your_module import getTupleIndex

class TestGetTupleIndex(unittest.TestCase):

    def setUp(self):
        # Sample graph branches: (u, v) pairs
        self.n_ij = [('A', 'B'), ('B', 'C'), ('C', 'D'), ('A', 'C')]

    def test_found_at_beginning(self):
        """Test when the target tuple is the first element."""
        self.assertEqual(getTupleIndex(self.n_ij, 'A', 'B'), 0)

    def test_found_in_middle(self):
        """Test when the target tuple is somewhere in the middle."""
        self.assertEqual(getTupleIndex(self.n_ij, 'B', 'C'), 1)

    def test_found_at_end(self):
        """Test when the target tuple is the last element."""
        self.assertEqual(getTupleIndex(self.n_ij, 'A', 'C'), 3)

    def test_not_found(self):
        """Test when the tuple does not exist in the list (should return None)."""
        self.assertIsNone(getTupleIndex(self.n_ij, 'X', 'Y'))

    def test_empty_list(self):
        """Test behavior when passed an empty list."""
        self.assertIsNone(getTupleIndex([], 'A', 'B'))

if __name__ == '__main__':
    unittest.main()