Added another unittest to test multiplication functionality

src/test/py/test_primitive_calculations.py

@@ -30,6 +30,9 @@ class primitive_calculations(unittest.TestCase):
     def test_multiply_5_multiply_5_equals_25(self):
         self.assertEqual(multiply(5, 5), 25)
 
+    def test_multiply_5_multiply_5_equals_5(self):
+        self.assertEqual(multiply(-5, -5), 25)
+
 
 if __name__ == "__main__":
     unittest.main()