@Test
    public void onError() {
        Throwable throwable = new Throwable("error");
        completeObserver.onError(throwable);
        ListenableFuture<Void> future = completeObserver.getCompletionFuture();
        assertThrows(Throwable.class, future::get);
    }
The Test Case For {@link CompleteObserver}.
shenyu-plugin/shenyu-plugin-proxy/shenyu-plugin-rpc/shenyu-plugin-grpc/src/test/java/org/apache/shenyu/plugin/grpc/proto/CompleteObserverTest.java