def test_equals(self):
     self.assertEqual(calculate_years(1000, 0.05, 0.18, 1100), 3)
 def test_equals_2(self):
     self.assertEqual(calculate_years(1000, 0.01625, 0.18, 1200), 14)
 def test_equals_3(self):
     self.assertEqual(calculate_years(1000, 0.05, .18, 1000), 0)