def test_two_values(self):
stats = RunningStats()
stats.add(4)
stats.add(6)
self.assertEqual(5, stats.average())
self.assertEqual(1, stats.variance())
def test_empty_case(self):
stats = RunningStats()
self.assertEqual(None, stats.average())
self.assertEqual(None, stats.variance())
def test_single_value(self):
stats = RunningStats()
stats.add(4)
self.assertEqual(4, stats.average())
self.assertEqual(0, stats.variance())
