is it a lambda arg thing?

rest_tools/server/arghandler.py

@@ -150,7 +150,7 @@ def _translate_error(
         captured_stderr: str,
     ) -> str:
         """Translate argparse-style error to a message str for HTTPError."""
-        LOGGER.error(f"Intercepted error to translate for requestor: {exc}")
+        LOGGER.error(f"Intercepted error to translate for requestor -> {exc}")
 
         # errors not covered by 'exit_on_error=False' (in __init__)
         if isinstance(exc, (SystemExit, argparse.ArgumentError)):

tests/unit_server/arghandler_test.py

@@ -643,7 +643,49 @@ def _error_it(_: Any, exc: Exception):
     "argument_source",
     [QUERY_ARGUMENTS, JSON_BODY_ARGUMENTS],
 )
-def test_235__argparse_custom_validation__argumenttypeerror__error(
+def test_240__argparse_custom_validation__argumenttypeerror__error(
+    argument_source: str,
+) -> None:
+    """Test `argument_source` arguments using argparse's advanced options."""
+    args: Dict[str, Any] = {
+        "foo": "True",
+    }
+    if argument_source == JSON_BODY_ARGUMENTS:
+        args = {
+            "foo": [1, 2, 3],
+        }
+
+    # set up ArgumentHandler
+    arghand = setup_argument_handler(
+        argument_source,
+        args,
+    )
+
+    def _error_it(_: Any):
+        raise argparse.ArgumentTypeError("it's a bad value and you *will* see this!")
+
+    for arg, _ in args.items():
+        print()
+        print(arg)
+        arghand.add_argument(
+            arg,
+            type=lambda x: _error_it(x),
+        )
+
+    with pytest.raises(tornado.web.HTTPError) as e:
+        arghand.parse_args()
+
+    assert (
+        str(e.value)
+        == "HTTP 400: argument foo: it's a bad value and you *will* see this!"
+    )
+
+
+@pytest.mark.parametrize(
+    "argument_source",
+    [QUERY_ARGUMENTS, JSON_BODY_ARGUMENTS],
+)
+def test_241__argparse_custom_validation__argumenttypeerror__error(
     argument_source: str,
 ) -> None:
     """Test `argument_source` arguments using argparse's advanced options."""