Issues with Mocking HttpURLConnection using Mockito

Question

I am trying to mock a HttpURLConnection object but I cant seem to get it right. Here is the method I would like to test.

@Override
public JSON connect() throws IOException {
    HttpURLConnection httpConnection;
    String finalUrl = url;
    URL urlObject = null;
    int status = 0;
    //recursively check for redirected uri if the given uri is moved
    do{
            urlObject = getURL(finalUrl);
            httpConnection = (HttpURLConnection) urlObject.openConnection();
            //httpConnection.setInstanceFollowRedirects(true);
            //httpConnection.connect();
            status = httpConnection.getResponseCode();
            if (300 > status && 400 < status){
                continue;
            }
            String redirectedUrl =    httpConnection.getHeaderField("Location");
            if(null == redirectedUrl){
                    break;
            }
            finalUrl =redirectedUrl;

    }while (httpConnection.getResponseCode() != HttpURLConnection.HTTP_OK);
    return  JSONSerializer.toJSON(getData(httpConnection).toString());
}

Here is what I have done.

 @Before
public void setUp() throws Exception{
    //httpConnectGithubHandle = new HttpConnectGithub(VALID_URL);
    httpConnectGithubHandle = mock(HttpConnectGithub.class);
    testURL               = new URL(VALID_URL);
    mockHttpURLConnection = mock(HttpURLConnection.class);  
    mockInputStreamReader = mock(InputStreamReader.class);
    mockBufferedReader    = mock(BufferedReader.class);
    mockInputStream       = mock(InputStream.class);
    when(httpConnectGithubHandle.getData(mockHttpURLConnection)).thenReturn(SOME_STRING);
    when(httpConnectGithubHandle.getURL(SOME_STRING)).thenReturn(testURL);
    when(mockHttpURLConnection.getResponseCode()).thenReturn(200);
    when(mockHttpURLConnection.getHeaderField(LOCATION)).thenReturn(SOME_STRING);
    PowerMockito.whenNew(InputStreamReader.class)
    .withArguments(mockInputStream).thenReturn(mockInputStreamReader);
    PowerMockito.whenNew(BufferedReader.class)
      .withArguments(mockInputStreamReader).thenReturn(mockBufferedReader);  
    PowerMockito.when(mockBufferedReader.readLine())
    .thenReturn(JSON_STRING)
    .thenReturn(null);
}

That was my setUp method. The test cases for methods that are called by this method are successful. And my actual test case is as follows.

 @Test
    public void testConnect() throws IOException {
        JSON jsonObject = httpConnectGithubHandle.connect();
        System.out.println(jsonObject);
        assertThat(jsonObject, instanceOf(JSON.class));
    }

I tried to print data, it shows null.

Answer 1

Currently your're only testing the mock. httpConnectGithubHandle.connect() is called on the mock and the mock returns null, because no behaviour is defined. You should use a real HttpConnectGithub object in your test. (Uncomment the first line of your test and remove the HttpConnectGithub mock.)