Add missing tests (zero case)

README.md

@@ -0,0 +1,25 @@
+# learn-git
+Hello Class!
+
+## Smaller head
+
+```js
+  function foo() {}
+```
+
+<details>
+ <summary> `package.json` </summary>
+
+```json
+
+{ "huge": "bunch of stuff" }
+
+```
+
+</details>
+
+<pre>
+<p align=center>
+  <a href="http://example.com"> Click me </a>
+</p>  
+</pre>

src/calc.py

@@ -5,6 +5,7 @@ def add(a, b, third_operand = 0):
     ```py
     add(2, 3) # 5
     add(2, 3, 4) # 9
+    hello
     ```
     """
     return a + b + third_operand

src/calc_test.py

@@ -17,6 +17,11 @@ 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(4, 3, 1), 0, 'subtracting three from one from four')
+
+    def test_sub_3arg_zeros(self):
+         self.assertEqual(sub(0, 0, 0), 0, 'zero minus zero minus zero is zero')
 
 if __name__ == '__main__':
     unittest.main()