GistFetcherTest.java

public class GistFetcherTest extends InstrumentationTestCase {
  public void testFetch() throws IOException {
    final InputStream mockResponseStream = getInstrumentation().getContext().getAssets().open("mock_response.json");

    OkHttpClient httpClient = new OkHttpClient();
    httpClient.interceptors().add(new Interceptor() {
      @Override
      public Response intercept(Chain chain) throws IOException {
        return new Response.Builder()
            .protocol(Protocol.HTTP_2)
            .code(200) // To make response.isSuccessful() return true.
            .request(chain.request())
            .body(new ResponseBody() {
              @Override
              public MediaType contentType() {
                return null;
              }

              @Override
              public long contentLength() {
                // Means we don't know the length beforehand.
                return -1;
              }

              @Override
              public BufferedSource source() {
                try {
                  return new Buffer().readFrom(mockResponseStream);
                } catch (IOException e) {
                  // Fail early!
                  Assertions.fail(e.getMessage(), e.getCause());
                  return null;
                }
              }
            })
            .build();
      }
    });

    // This will be ignored. We won't execute any network request for it.
    String url = "https://api.github.com/gists/AWESOME_GIST_ID";
    GistFetcher fetcher = new GistFetcher(httpClient, new Gson());
    GistFetcher.Gist gist = fetcher.fetch(url);

    assertThat(gist).isNotNull();
    assertThat(gist.files()).hasSize(2).containsKeys("ObservableProperty.java", "usage.md");
  }
}