test.py

def test_returns_2_when_x_is_1_and_y_is_1(self):
  self.assertEqual(2, sum(1, 2))

def test_returns_1_when_x_is_2_and_y_is_neg1(self):
  self.assertEqual(1, sum(2, -1))

# etc....

# versus:

def test_adds_two_integers(self):
  self.assertEqual(2, sum(1, 2))
  self.assertEqual(1, sum(2, -1))
  # etc...

# you may have heard "only assert one thing"
# that doesn't always mean only have one literal assertion call in your test
# it means only have one logical assertion
# i.e. test the smallest unit of logic that matters
# that sometimes requires multiple assert calls for very low-level functions