Print the key name when max_length is exceeded (#43061)

* Print the key name when max_length is exceeded

* Fix tests

airflow/utils/helpers.py

@@ -50,7 +50,7 @@ def validate_key(k: str, max_length: int = 250):
     if not isinstance(k, str):
         raise TypeError(f"The key has to be a string and is {type(k)}:{k}")
     if len(k) > max_length:
-        raise AirflowException(f"The key has to be less than {max_length} characters")
+        raise AirflowException(f"The key: {k} has to be less than {max_length} characters")
     if not KEY_REGEX.match(k):
         raise AirflowException(
             f"The key {k!r} has to be made of alphanumeric characters, dashes, "

tests/utils/test_helpers.py

@@ -203,7 +203,7 @@ def test_build_airflow_url_with_query(self):
                 "characters, dashes, dots and underscores exclusively",
                 AirflowException,
             ),
-            (" " * 251, "The key has to be less than 250 characters", AirflowException),
+            (" " * 251, f"The key: {' ' * 251} has to be less than 250 characters", AirflowException),
         ],
     )
     def test_validate_key(self, key_id, message, exception):

tests/www/test_validators.py

@@ -151,7 +151,7 @@ def test_validation_fails_with_too_many_characters(self):
 
         with pytest.raises(
             validators.ValidationError,
-            match=r"The key has to be less than [0-9]+ characters",
+            match=r"The key: [x]+ has to be less than [0-9]+ characters",
         ):
             self._validate()