diff --git a/src/calc_test.py b/src/calc_test.py
index 2911910..255bfb7 100644
--- a/src/calc_test.py
+++ b/src/calc_test.py
@@ -16,7 +16,9 @@ def test_add_zeroes(self):
     def test_sub_2arg(self):
         # Make sure 4 - 3 = 1
         self.assertEqual(sub(4, 3), 1, 'subtracting three from four')
-
+        
+    def sub (a, b, c=0):
+    return a - b - c 
 
 if __name__ == '__main__':
     unittest.main()