Add test case for issue #934

Reviewed By: yangdanny97

Differential Revision: D80379943

fbshipit-source-id: 223dc9af77d60e63efb523b4d98f1d4070fe7b0a

Author: rchen152

pyrefly/lib/test/named_tuple.rs

@@ -347,3 +347,17 @@ class B(A):
         return super().__init__(x, y)
 "#,
 );
+
+testcase!(
+    bug = "The asserted type is wrong",
+    test_custom_iter,
+    r#"
+from typing import assert_type, Iterator, NamedTuple
+class NT(NamedTuple):
+    x: int
+    def __iter__(self) -> Iterator[str]: ...
+nt = NT(0)
+for x in nt:
+    assert_type(x, str)  # E: assert_type(int, str)
+    "#,
+);