Fix typing issues

src/graphql/execution/map_async_iterator.py

@@ -2,7 +2,7 @@
 from concurrent.futures import FIRST_COMPLETED
 from inspect import isasyncgen, isawaitable
 from types import TracebackType
-from typing import Any, AsyncIterable, Callable, Optional, Set, Type, Union, cast
+from typing import Any, AsyncIterable, Callable, Optional, Set, Type, Union
 
 __all__ = ["MapAsyncIterator"]
 
@@ -85,11 +85,7 @@ async def athrow(
             if value is None:
                 if traceback is None:
                     raise type_  # pragma: no cover
-                value = (
-                    type_
-                    if isinstance(value, BaseException)
-                    else cast(Type[BaseException], type_)()
-                )
+                value = type_ if isinstance(value, BaseException) else type_()
             if traceback is not None:
                 value = value.with_traceback(traceback)
             raise value

tests/execution/test_subscribe.py

@@ -1,7 +1,12 @@
 import asyncio
 from typing import Any, Callable, Dict, List
 
-from graphql.execution import MapAsyncIterator, create_source_event_stream, subscribe
+from graphql.execution import (
+    ExecutionResult,
+    MapAsyncIterator,
+    create_source_event_stream,
+    subscribe,
+)
 from graphql.language import parse
 from graphql.pyutils import SimplePubSub
 from graphql.type import (
@@ -446,6 +451,8 @@ async def resolves_to_an_error_if_variables_were_wrong_type():
         # resolve to an ExecutionResult that contains an informative error description.
         result = await subscribe(schema, document, variable_values=variable_values)
 
+        assert isinstance(result, ExecutionResult)
+
         assert result == (
             None,
             [
@@ -457,7 +464,9 @@ async def resolves_to_an_error_if_variables_were_wrong_type():
             ],
         )
 
-        assert result.errors[0].original_error
+        errors = result.errors
+        assert errors
+        assert errors[0].original_error
 
 
 # Once a subscription returns a valid AsyncIterator, it can still yield errors.