How to test IOException case in OkHttp?

Question

I am trying to test my codebase in the event OkHttpClient throws an IOException

Code under test

    try (var response = okHttpClient.newCall(request).execute()) {
        return response;
    } catch (final IOException e) {
        log.error("IO Error from API", e);
        throw new ApiException(e.getMessage(), e);
    }

Test

@Test
void createCustomer_WhenValidRequestAndIOException_ThenThrowAPIException() throws ZeusServiceException, ZeusClientException {

    //Given
    final OkHttpClient okHttpClientMock = mock(OkHttpClient.class, RETURNS_DEEP_STUBS);
    final OkHttpClient.Builder okHttpBuilderMock = mock(OkHttpClient.Builder.class);
    httpClient = new HttpClient(okHttpClientMock, configuration, objectMapper);

    //When
    when(okHttpClientMock.newBuilder()).thenReturn(okHttpBuilderMock);
    when(okHttpBuilderMock.build()).thenReturn(okHttpClientMock);
    when(okHttpClientMock.newCall(any())).thenThrow(IOException.class);
    final var result = httpClient.createCustomer(request);

    assertThatThrownBy(() -> httpClient.createCustomer(request))
        .isInstanceOf(ApiException.class)
        .hasMessage("IO Error from API");
}

I tried to mock the OkHttpClient and Builder class, however Builder is final, and mockito cannot mock it.

In the constructor of the class under test, you are recommended to create a new instance of OkHttpClient by invoking this

        this.okHttpClient = okHttpClient.newBuilder().build();

I tried to create a wrapper around OkHttpClient but that didn't work either

    public class OkHttpClientWrapper extends OkHttpClient {

        private OkHttpClient okHttpClient;

        public OkHttpClientWrapper(final OkHttpClient okHttpClient) {
            this.okHttpClient = okHttpClient;
        }

        @Override
        public OkHttpClient.Builder newBuilder() {
            return new Builder(okHttpClient);
        }
    }
}

How can I force okhttpclient to throw an IOException?

Yea but people say PowerMockito is evil https://stackoverflow.com/questions/30162200/why-not-powermock — tomaytotomato, Aug 23 '21 at 16:38
maybe creating a `Factory` for `OkHttpClient` and then mocking that `Factory`? — Alberto Sinigaglia, Aug 23 '21 at 16:38
Have you considered not mocking it at all, but looking up how OkHttp recommends you test this case? — Louis Wasserman, Aug 23 '21 at 16:42
@tomaytotomato Did you read the answers behind it? It suggests a design issue. However, these are not your types. You can't redesign those types to be more easily tested in a natural manner. There could be other ways to handle the situation (as Louis recommends), but rejecting PowerMockito just because you read on the internet that it's evil, without diving into _why_ it's evil, may lead you to writing more complex test code than actually needed. — Vince, Aug 23 '21 at 16:50
Doesn't change the fact though that PowerMock *is* evil, and that the 2021 answer to unit testing restful endpoints is rather to use something like https://github.com/square/okhttp/tree/master/mockwebserver instead. — GhostCat, Aug 24 '21 at 09:59
@GhostCat indeed there is a way in MockWebServer to simulate a closed/terminated connection, which covers the test scenario. Please see submitted answer — tomaytotomato, Aug 24 '21 at 16:33

score 7 · Accepted Answer · answered Aug 24 '21 at 16:30

In the end the best solution was to leverage OkHttp's MockWebServer

https://github.com/square/okhttp/tree/master/mockwebserver

Using a scenario where MockWebserver unexpectedly terminates the HTTP connection, causes an IOException scenario

@Test
void createCustomer_WhenValidRequestAndServerTerminatesConnection_ThenThrowIOException() throws ZeusServiceException, ZeusClientException {

    //Given
    final CreateCustomerRequest request = CreateCustomerRequest.builder().build();

    //When
    mockWebServer.enqueue(new MockResponse()
        .setBody(new Buffer().write(new byte[4096]))
        .setSocketPolicy(SocketPolicy.DISCONNECT_DURING_RESPONSE_BODY));

    assertThatThrownBy(() -> httpClient.createCustomer(request))
        .isInstanceOf(IOException.class)
        .hasMessage("unexpected end of stream");
}

Note: use of AssertJ library in this test

Wojtek · Answer 2 · 2021-08-24T10:32:58.850

You have a few options:

Use Powermock with Mockito to mock the final elements. This will allow you to unit-test all of your code.
You can use Wiremock or a similar over-the-wire HTTP mocking tool which will allow you to test all of your code in a black-box fashion. All of your code can be tested this way as a black box.
Refactor you're code and wrap OkHttp classes and methods in your own classes that can be mocked. This still leaves some code untested.

How to test IOException case in OkHttp?

2 Answers2