Fix Galaxy paging review findings

clients/python/tests/test_galaxy.py

@@ -148,6 +148,22 @@ async def test_discover_hierarchy_returns_proto_objects() -> None:
     assert objects[1].attributes[0].full_tag_reference == "DelmiaReceiver_001.DownloadPath"
 
 
+@pytest.mark.asyncio
+async def test_discover_hierarchy_rejects_repeated_page_token() -> None:
+    stub = FakeGalaxyStub()
+    stub.discover_hierarchy.replies = [
+        galaxy_pb.DiscoverHierarchyReply(next_page_token="7:1"),
+        galaxy_pb.DiscoverHierarchyReply(next_page_token="7:1"),
+    ]
+    client = await GalaxyRepositoryClient.connect(
+        ClientOptions(endpoint="fake", plaintext=True),
+        stub=stub,
+    )
+
+    with pytest.raises(Exception, match="repeated page token"):
+        await client.discover_hierarchy()
+
+
 @pytest.mark.asyncio
 async def test_watch_deploy_events_yields_events_in_order() -> None:
     ts1 = Timestamp()