Retrofit: [Feature request] Mocking for Call<Void> responses

[Yukiatsu]

Given the following example:

public interface Example {
    @GET
    public Call<MyObject> getThingy();
        @POST
        public Call<Void> postThingy();
}

to mock the response for the GET request, I do something like:

MyObject object = new MyObject();
Call<MyObject> response = Calls.response(object);
when(example.getThingy()).thenReturn(response);

But when I try to do the same for the second request

Constructor<Void> voidConstructor = Void.class.getDeclaredConstructor();
voidConstructor.setAccessible(true);
Void voidMock = voidConstructor.newInstance();
Call<Void> response = Calls.response(voidMock);
when(example.postThingy()).thenReturn(response);

NPE is thrown (I tried some other approaches to this, but every time NPE was thrown; this was the one most likely to work) at response.enqueue

        response.enqueue(new Callback<Void>() {
            @Override
            public void onResponse(Call<Void> call, Response<Void> response) {
               //Do something
            }

            @Override
            public void onFailure(Call<Void> call, Throwable t) {
                //Do something
            }
        });

Is it possible for Call<Void> response = Calls.response(voidMock); to return a response that will not throw a NPE? (or maybe there is another way to test the postThingy() method; I didn't manage to find any, since there is scarce info on how to mock Call<> responses... took me a lot of time to find what I wrote above).

[JakeWharton]

Void is an instance-less type in Java. The only value value for it is null. You should use Calls.response(null). This method was missing a @Nullable annotation which has been fixed on master and will go out with 2.3.0 which should be in the next week or two.

[Yukiatsu]

Thank you for fast and clear reply. Will be waiting for the next version. Good luck and happy coding.

[Yukiatsu]

Hi @JakeWharton
This issue is not fixed in version 2.3.0. Calls.response(null) throws an AssertionError with the following message: Only one of response or error can be set. (the message is not accurate nor suggestive)
From what i saw, FakeCall class is not handling response == null cases yet, so can you please re-open the issue, or write a comment with an update on the issue?

[JakeWharton]

I meant 2.4.0

[jaredculp]

This still doesn't work on 2.4.0 since FakeCall expects at least one of the response or error to be non-null.

[NightlyNexus]

@jaredculp
make sure you're linking to the correct method. https://github.com/square/retrofit/blob/5c2f505a974d84763b3c2279128351b8a73a3e2d/retrofit-mock/src/main/java/retrofit2/mock/Calls.java#L37
and not https://github.com/square/retrofit/blob/5c2f505a974d84763b3c2279128351b8a73a3e2d/retrofit-mock/src/main/java/retrofit2/mock/Calls.java#L41

[jaredculp]

Thanks @NightlyNexus, looks like the compiler just needed a bit of help:

interface Client {
  Call<Void> request();
}

when(client.request()).thenReturn(Calls.response((Void) null));