added example with test

Author: sgpearson17

example.py

@@ -2,4 +2,8 @@ def add(a, b):
     return a + b
 
 def subtract(a, b):
-    return a + b  # do not change this line until prompted to do so.
+    return a + b  # do not change this line until prompted to do so.
+    
+def test_add():
+	assert add(1,2)==3
+	# assert add(2,3)==0