Mock external dependency that returns a Future of list

Question

I have a class which have external dependency that returns future of lists. How to mock the external dependency?

 public void meth() {
     //some stuff
     Future<List<String>> f1 = obj.methNew("anyString")
     //some stuff
 }

 when(obj.methNew(anyString()).thenReturn("how to intialise some data here, like list of names")

Maybe `thenAnswer` is what you need here instead of `thenReturn`. [This answer](https://stackoverflow.com/a/36627077/1744230) explains the difference between those two. — QBrute, Jul 28 '17 at 20:21

score 25 · Answer 1 · answered Jul 28 '17 at 20:27

25

You can create the future and return it using thenReturn(). In the case below, I create an already completed Future<List<String>> using CompletableFuture.

when(f1.methNew(anyString()))
        .thenReturn(CompletableFuture.completedFuture(Arrays.asList("A", "B", "C")));

answered Jul 28 '17 at 20:27

Todd

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Similarly, how o return for Call call = obji.methNew(B). – user304611 Jul 28 '17 at 20:39

score 12 · Answer 2 · answered Jul 29 '17 at 06:41

As alternative way you may mock the Future as well. The benefit of such way is ability to define any behavior.

For example you want to test a case when a task was canceled:

final Future<List<String>> mockedFuture = Mockito.mock(Future.class);
when(mockedFuture.isCancelled()).thenReturn(Boolean.TRUE);
when(mockedFuture.get()).thenReturn(asList("A", "B", "C"));

when(obj.methNew(anyString()).thenReturn(mockedFuture);

Mock external dependency that returns a Future of list

2 Answers2