Add tests for str.__iter__ and str.__next__

tests/snippets/strings.py

@@ -263,3 +263,33 @@ assert "\u0041" == "A"
 assert "\u00BE" == "¾"
 assert "\u9487" == "钇"
 assert "\U0001F609" == "😉"
+
+# test str iter
+iterable_str = "123456789"
+str_iter = iter(iterable_str)
+
+assert next(str_iter) == "1"
+assert next(str_iter) == "2"
+assert next(str_iter) == "3"
+assert next(str_iter) == "4"
+assert next(str_iter) == "5"
+assert next(str_iter) == "6"
+assert next(str_iter) == "7"
+assert next(str_iter) == "8"
+assert next(str_iter) == "9"
+assert next(str_iter, None) == None
+assert_raises(StopIteration, lambda: next(str_iter))
+
+str_iter_reversed = reversed(iterable_str)
+
+assert next(str_iter_reversed) == "9"
+assert next(str_iter_reversed) == "8"
+assert next(str_iter_reversed) == "7"
+assert next(str_iter_reversed) == "6"
+assert next(str_iter_reversed) == "5"
+assert next(str_iter_reversed) == "4"
+assert next(str_iter_reversed) == "3"
+assert next(str_iter_reversed) == "2"
+assert next(str_iter_reversed) == "1"
+assert next(str_iter_reversed, None) == None
+assert_raises(StopIteration, lambda: next(str_iter_reversed))