How to throw an exception on an CompletableFuture.get() call?

Question

Is there a way to have mockito throw an exception on the CompletableFuture.get() call and not just the asynchronous method?

For example, given the following (incorrect) test case:

@Test
public void whenRunnerThrows_thenReturn5xx() throws Exception {
    when(service.runAsync(any(),any())).thenThrow(new Exception(""));

    mvc.perform(post("/test")
            .contentType(MediaType.APPLICATION_JSON)
            .content("{\"name\":\"test\"}"))
            .andExpect(status().is5xxServerError());
}

When service.runAsync() is called during testing, an exception is thrown, which makes sense. But when the (Spring Boot) application is run, then the same exception will only be thrown as a an ExecutionException cause on the returned CompletableFuture::get.

What is the correct way to write a test like this one so that the exception is thrown at the same time in unit testing as it is when running the application?

Answer 1

As Sotirios pointed out, you can create a CompletableFuture and have it complete with the exception. Here's the code for reference to others:

@Test
public void whenRunnerThrows_thenReturn5xx() throws Exception {
    CompletableFuture<String> badFuture = new CompletableFuture<>();
    badFuture.completeExceptionally(new Exception(""));
    when(service.runAsync(any(),any())).thenReturn(badFuture);

    mvc.perform(post("/test")
            .contentType(MediaType.APPLICATION_JSON)
            .content("{\"name\":\"test\"}"))
            .andExpect(status().is5xxServerError());
}