How to mock Jersey REST client to throw HTTP 500 responses?

Question

I am writing a Java class that uses Jersey under the hood to send an HTTP request to a RESTful API (3rd party).

I would also like to write a JUnit test that mocks the API sending back HTTP 500 responses. Being new to Jersey, it is tough for me to see what I have to do to mock these HTTP 500 responses.

So far here is my best attempt:

// The main class-under-test
public class MyJerseyAdaptor {
    public void send() {
        ClientConfig config = new DefaultClientConfig();
        Client client = Client.create(config);
        String uri = UriBuilder.fromUri("http://example.com/whatever").build();
        WebResource service = client.resource(uri);

        // I *believe* this is where Jersey actually makes the API call...
        service.path("rest").path("somePath")
                .accept(MediaType.TEXT_HTML).get(String.class);
    }
}

@Test
public void sendThrowsOnHttp500() {
    // GIVEN
    MyJerseyAdaptor adaptor = new MyJerseyAdaptor();

    // WHEN
    try {
        adaptor.send();

        // THEN - we should never get here since we have mocked the server to
        // return an HTTP 500
        org.junit.Assert.fail();
    }
    catch(RuntimeException rte) {
        ;
    }
}

I am familiar with Mockito but have no preference in mocking library. Basically if someone could just tell me which classes/methods need to be mocked to throw a HTTP 500 response I can figure out how to actually implement the mocks.

Answer 1

Try this:

WebResource service = client.resource(uri);

WebResource serviceSpy = Mockito.spy(service);

Mockito.doThrow(new RuntimeException("500!")).when(serviceSpy).get(Mockito.any(String.class));

serviceSpy.path("rest").path("somePath")
            .accept(MediaType.TEXT_HTML).get(String.class);

I don't know jersey, but from my understanding, I think the actual call is done when get() method is invoked. So you can just use a real WebResource object and replace the behavior of the get(String) method to throw the exception instead of actually execute the http call.