Change "yield" to "produce"

Author: cjyuan

Sprint-3/1-implement-and-rewrite-tests/testing-guide.md

@@ -9,7 +9,7 @@ Input  ──▶  Function  ──▶  Output
 A function
 - Takes **input** (via **arguments**)
 - Does some work
-- Yields **one output** (via a **return value**)
+- Produces **one output** (via a **return value**)
 
 Example: