Revert "remove test case"

This reverts commit d4264c7.

Author: mmcky

lectures/aiyagari.md

@@ -34,6 +34,14 @@ In addition to what's in Anaconda, this lecture will need the following librarie
 !pip install quantecon
 ```
 
+```{code-cell} ipython3
+import warnings
+warnings.warn(
+        "This function will be deprecated in a future version. ",
+        FutureWarning
+    )
+```
+
 ## Overview
 
 In this lecture, we describe the structure of a class of models that build on work by Truman Bewley {cite}`Bewley1977`.