Fix tag duplication when using cbv

fastapi_restful/cbv.py

@@ -85,6 +85,15 @@ def new_init(self: Any, *args: Any, **kwargs: Any) -> None:
     setattr(cls, CBV_CLASS_KEY, True)
 
 
+def _remove_router_tags(route: Route, router: APIRouter) -> None:
+    """
+    Removes tags previously assigned to the route by the router, as they will
+    be added again later when re-added to the router.
+    """
+    if hasattr(route, 'tags'):
+        route.tags = list(set(route.tags) - set(router.tags))
+
+
 def _register_endpoints(router: APIRouter, cls: Type[Any], *urls: str) -> None:
     cbv_router = APIRouter()
     function_members = inspect.getmembers(cls, inspect.isfunction)
@@ -111,6 +120,7 @@ def _register_endpoints(router: APIRouter, cls: Type[Any], *urls: str) -> None:
     prefix_length = len(router.prefix)  # Until 'black' would fix an issue which causes PEP8: E203
     for route in cbv_routes:
         router.routes.remove(route)
+        _remove_router_tags(route, router)
         route.path = route.path[prefix_length:]
         _update_cbv_route_endpoint_signature(cls, route)
         cbv_router.routes.append(route)

tests/test_cbv.py

@@ -130,3 +130,14 @@ def root(self) -> str:
         response = client.get("/api/item")
         assert response.status_code == 200
         assert response.json() == "hello"
+
+    def test_duplicate_tag_removal(self) -> None:
+        router = APIRouter(prefix="/api", tags=["test"])
+
+        @cbv(router)
+        class CBV:
+            @router.get("/item")
+            def root(self) -> str:
+                return "hello"
+
+        assert router.routes[0].tags == ["test"]