===== Testing add =====
2/3 + 1/6 = 5/6
1/5 + 4/9 = 29/45
3/7 + 12/21 = 1/1
5/8 + 3/16 = 13/16
7/8 + 3/12 = 9/8
0/8 + 3/16 = 3/16
1/1 + 3/16 = 19/16
5/8 + -3/16 = 7/16
1/5 + -4/9 = -11/45
-1/5 + -4/9 = -29/45
1/2 + 1/2 = 1/1
5/5 + -5/5 = 0/1