### Question:
FutureBackupCallback extends IBackupCallback.Stub { @Override public void operationComplete(long result) throws RemoteException { mFuture.complete(RemoteResult.of(result)); } FutureBackupCallback(CompletableFuture<RemoteResult> future); @Override void operationComplete(long result);  }### Answer:
@Test public void testOperationComplete_completesFuture() throws Exception { CompletableFuture<RemoteResult> future = new CompletableFuture<>(); FutureBackupCallback callback = new FutureBackupCallback(future); callback.operationComplete(7); assertThat(future.get()).isEqualTo(RemoteResult.of(7)); }