diff --git a/src/calc_test.py b/src/calc_test.py
index 2911910..6f54028 100644
--- a/src/calc_test.py
+++ b/src/calc_test.py
@@ -17,6 +17,7 @@ def test_sub_2arg(self):
         # Make sure 4 - 3 = 1
         self.assertEqual(sub(4, 3), 1, 'subtracting three from four')
 
-
+    def test_sub_3arg(self):
+        self.assertEqual(sub(3, 5, 2), -4, 'subtracting three, five and two')
 if __name__ == '__main__':
     unittest.main()