fix: fix typing issue with gRPC metadata when key ends in

tests/system/test_request_metadata.py

@@ -0,0 +1,38 @@
+# Copyright 2018 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from google import showcase
+
+def test_metadata_string(echo):
+    echo.echo(
+        showcase.EchoRequest(
+            content="The hail in Wales falls mainly on the snails.",
+            request_id="some_value",
+            other_request_id="",
+        ),
+        metadata=[('some-key', 'some_value')]
+    )
+
+# See https://github.com/googleapis/gapic-generator-python/issues/2250
+# When the metadata key ends in `-bin`, the value should be of type
+# `bytes`` rather than `str``.
+def test_metadata_binary(echo):
+    echo.echo(
+        showcase.EchoRequest(
+            content="The hail in Wales falls mainly on the snails.",
+            request_id="some_value",
+            other_request_id="",
+        ),
+        metadata=[('some-key-bin', 'some_value')]
+    )