Added more test files from lectures.

test21.py

@@ -0,0 +1,17 @@
+from random import random
+class EvilDescriptor:
+    i: int
+
+    def __init__(self, i) -> None:
+        self.i = i
+
+    def __set__(self, instance, i: int):
+        self.instance = i + (random()*10)-5
+
+    def __index__(self):
+        return int(self.i)
+
+if __name__ == '__main__':
+    evil = EvilDescriptor(3)
+    evil.i = 5
+    print(f"{int(evil)=}")