Тесты Junit для настраиваемого фильтра сервлетов с помощью Spring

Question

У меня есть простой фильтр, который обрабатывает ответ следующим образом.

public class CustomInjectFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // No implementation needed
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
        try {
            PrintWriter originalOutWriter = response.getWriter();
            // Custom wrapper to get the response
            CustomResponseWrapper responseWrapper = new CustomResponseWrapper((HttpServletResponse) response);
            // Continue to process everything in the chain
            filterChain.doFilter(request, responseWrapper);

            // Add to the original response
            StringWriter newWriter = new StringWriter();
            String originalContent = responseWrapper.getResponseContent();

            // Conver to json
            Gson gson = new GsonBuilder().registerTypeAdapter(Pojo.class, new CustomDataSerializer()).create();
            // At this point I do some custom stuff like adding few attributes to Pojo class before transforming it back to json.

            newWriter.write(gson.toJson(str));
            response.setContentLength(newWriter.toString().length());
            originalOutWriter.write(newWriter.toString());
            originalOutWriter.close();
        } catch (Exception e) {
            throw new IllegalArgumentException("Unable to serialize/deserialize data");
        }
    }


    @Override
    public void destroy() {
        // No implementation needed
    }
}

Регистрация его с помощью

@Configuration
public class CustomConfiguration {

    @Bean
    @Order(Ordered.HIGHEST_PRECEDENCE)
    public FilterRegistrationBean custFilterRegistrationBean() {
        CustomInjectFilter filter = new CustomInjectFilter();
        FilterRegistrationBean bean = new FilterRegistrationBean();
        bean.setFilter(filter);
        List<String> match = new ArrayList<>();
        match.add("**/setup/*");
        bean.setUrlPatterns(match);
        return bean;
    }
}

Junit-тестов,

@RunWith(SpringRunner.class)
@ContextConfiguration(classes = {TestConfiguration.class})
public class CustomInjectFilterITest {

    @Test
    public void testDoFilter() throws ServletException, IOException {

        CustomInjectFilter filter = new CustomInjectFilter();

        HttpServletRequest mockReq = Mockito.mock(HttpServletRequest.class);
        HttpServletResponse mockResp = Mockito.mock(HttpServletResponse.class);
        FilterChain mockFilterChain = Mockito.mock(FilterChain.class);
        FilterConfig mockFilterConfig = Mockito.mock(FilterConfig.class);
        Mockito.when(mockReq.getRequestURI()).thenReturn("/setup");

        final StringWriter stringWriter = new StringWriter();
        final PrintWriter writer = new PrintWriter(stringWriter);
        writer.print("{\"source\":\"testdata\"}");
        Mockito.when(mockResp.getWriter()).thenReturn(writer);

        filter.init(mockFilterConfig);
        filter.doFilter(mockReq, mockResp, mockFilterChain);
        filter.destroy();
    }
}

IЯ совершенно не уверен, правильно ли я написал этот тест, поскольку responseWrapper.getResponseContent() всегда пуст.

Правильно ли я настроил этот модульный тест?