Mocking API Responses using a Retrofit Client in Android

RestServiceMockUtils.java

public class RestServiceMockUtils {

    public static String convertStreamToString(InputStream is) throws Exception {
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line).append("\n");
        }
        reader.close();
        return sb.toString();
    }

    public static String getStringFromFile(Context context, String filePath) throws Exception {
        final InputStream stream = context.getResources().getAssets().open(filePath);

        String ret = convertStreamToString(stream);
        //Make sure you close all streams.
        stream.close();
        return ret;
    }

    public static RetrofitMockClient getClient(Context context, final int httpStatusCode, String reason, String responseFileName) throws Exception {
        return new RetrofitMockClient(httpStatusCode, reason, getStringFromFile(context, responseFileName));
    }
}

quote_401_unauthorised.json

{
  "error": {
    "code": 401,
    "message": "Unauthorized"
  }
}

QuoteOfTheDayServiceTests.java

public class QuoteOfTheDayServiceTests extends InstrumentationTestCase {
   public static final TAG = "QODServiceTest";
   public static final String BASE_API_URL = "http://api.theysaidso.com/";
    @SmallTest
    public void testAuthoriseFailsForIncorrectSessionId() throws Exception {
        String jsonResponseFileName = "quote_401_unauthorised.json";
        int expectedHttpResponse = 401;
        String reason = "Unauthorised";
        //Create RetrofitMockClient with the expected JSON response and code.
        RetrofitMockClient retrofitMockClient = RestServiceMockUtils.getClient(getInstrumentation().getContext(), expectedHttpResponse, reason, jsonResponseFileName);

        RestAdapter restAdapter = new RestAdapter.Builder()
                .setEndpoint(BASE_API_URL)
                .setClient(retrofitMockClient)
                .setConverter(new JacksonConverter())
                .setErrorHandler(new RetrofitErrorHandler())
                .build();

        RestService restServiceClient = restAdapter.create(RestService.class);

        //Run test code - you can test anything you want to here, test the correct response, the way the UI displays for certain mock JSON.
        String incorrectApiKey = "incorrectApiKey";
        try {
            String quote = restServiceClient.getQuoteOfTheDay(incorrectApiKey);
            Assert.fail("Should have thrown unauthorised exception");
        } catch (UnauthorizedException unauthorised) {
            Log.d(TAG, "Successfully caught unauthorised exception when incorrect API key was passed");
        }
        
    }

}

RetrofitMockClient.java

public class RetrofitMockClient implements Client {

    private String jsonResponse;
    private int statusCode = 200;
    private String reason;
    private static final String MIME_TYPE = "application/json";

    public RetrofitMockClient(int statusCode, String reason, String jsonResponse) {
        this.statusCode = statusCode;
        this.reason = reason;
        this.jsonResponse = jsonResponse;
    }

    @Override
    public Response execute(Request request) throws IOException {
        return createDummyJsonResponse(request.getUrl(), statusCode, reason, jsonResponse);
    }

    private Response createDummyJsonResponse(String url, int responseCode, String reason, String json) {
        return new Response(url, responseCode, reason, Collections.EMPTY_LIST,
                new TypedByteArray(MIME_TYPE, json.getBytes()));
    }

}