add errorhandler type check tests

tests/typing/typing_error_handler.py

@@ -0,0 +1,33 @@
+from __future__ import annotations
+
+from http import HTTPStatus
+
+from werkzeug.exceptions import BadRequest
+from werkzeug.exceptions import NotFound
+
+from flask import Flask
+
+app = Flask(__name__)
+
+
+@app.errorhandler(400)
+@app.errorhandler(HTTPStatus.BAD_REQUEST)
+@app.errorhandler(BadRequest)
+def handle_400(e: BadRequest) -> str:
+    return ""
+
+
+@app.errorhandler(ValueError)
+def handle_custom(e: ValueError) -> str:
+    return ""
+
+
+@app.errorhandler(ValueError)
+def handle_accept_base(e: Exception) -> str:
+    return ""
+
+
+@app.errorhandler(BadRequest)
+@app.errorhandler(404)
+def handle_multiple(e: BadRequest | NotFound) -> str:
+    return ""