tests: properly handle closed client in testproxy

Author: feywind

testproxy/services/sample-row-keys.ts

@@ -42,11 +42,11 @@ export const sampleRowKeys: ClientImplMaker<
       };
     } catch (e) {
       const error = e as GoogleError;
-      console.error('Error:', error.code);
 
       return {
         status: {
-          code: error.code,
+          // This might be zero/undefined if it's a disconnected client error.
+          code: error.code || grpc.status.FAILED_PRECONDITION,
           details: [],
         },
       };