Question

I have the following class which contains a hard coded URL that never changes:

    public class HttpClient {
        private final String DOWNLOAD_URL = "http://original.url.json";

        public String readJsonDataFromUrl() throws IOException {
            URLConnection urlConnection = getUrlConnection();

            BufferedReader reader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
            StringBuffer content = new StringBuffer();

            String readLine = "";
            while ((readLine = reader.readLine()) != null)  {
                content.append(readLine);
            }

            return content.toString();
        }

        private URLConnection getUrlConnection() throws IOException {
            URL jsonLocator = new URL(DOWNLOAD_URL);

            return jsonLocator.openConnection();
        }
    }

Now imagine that I’d like to expect the IOException in my test. In my opinion, the only way to do that is to rewrite the complete class in a mock object because of the final variable:

public class HttpClientMock extends HttpClient  {
    private final String DOWNLOAD_URL = "http://wrong.test.url.json";

    @Override
    public String readJsonDataFromUrl() throws IOException {
        URLConnection urlConnection = getUrlConnection();

        BufferedReader reader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
        StringBuffer content = new StringBuffer();

        String readLine = "";
        while ((readLine = reader.readLine()) != null)  {
            content.append(readLine);
        }

        return content.toString();
    }

    private URLConnection getUrlConnection() throws IOException {
        URL jsonLocator = new URL(DOWNLOAD_URL);
        URLConnection urlConnection = jsonLocator.openConnection();

        return urlConnection;
    }
}

But this is somehow far-fetched. If the original methods would be changed, the test results could still be positive because with this attempt, I don’t actually test the original class anymore.

How can this be done properly? (I don’t want to use a framework just for this one test, so are there any design attempts to solve this in a common way?)

Answer 1

Thanks to everybody, but I think that Gilbert Le Blanc’s solution is the most preferable for that case which looks like this:

The original class:

public class HttpClient {
    private final String DOWNLOAD_URL = "http://my.original.json.url";

    public String readJsonDataFromUrl() throws IOException {
        URLConnection urlConnection = getUrlConnection();

        BufferedReader reader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
        StringBuffer content = new StringBuffer();

        String readLine = "";
        while ((readLine = reader.readLine()) != null)  {
            content.append(readLine);
        }

        return content.toString();
    }

    private URLConnection getUrlConnection() throws IOException {
        URL jsonLocator = new URL(getConnectionString());

        return jsonLocator.openConnection();
    }

    protected String getConnectionString()  {
        return DOWNLOAD_URL;
    }
}

The mock object:

public class HttpClientMock extends HttpClient  {
    private String downloadUrl = "http://my.original.json.url";

    public HttpClientMock()  {
        super();
    }

    public HttpClientMock(String downloadUrl)  { 
        this.downloadUrl = downloadUrl;
    }

    @Override
    protected String getConnectionString()  {
        return downloadUrl;
    }
}

And the working tests:

public class HttpClientTest {

    private JSONParser jsonParser = new JSONParser();

    @Test
    public void readJsonDataFromUrlSucceeds() throws IOException, ParseException {
        HttpClient httpClient = new HttpClientMock();

        String jsonString = httpClient.readJsonDataFromUrl();
        JSONObject jsonObject = (JSONObject)jsonParser.parse(jsonString);

        assertTrue(jsonObject.size() > 0);
    }

    @Test(expected = IOException.class)
    public void readJsonDataFromMalformedUrlFails() throws IOException, ParseException {
        HttpClient httpClient = new HttpClientMock("http://malformed");

        httpClient.readJsonDataFromUrl();
    }
}