Question

This is the class that I have to test:

public class Downloader {
  public String download(String uri) {
    HttpClient client = this.getHttpClient();
    client.setURI(uri);
    return client.get();
  }
  private HttpClient getHttpClient() {
    HttpClient client = new HttpClient();
    // + some config
    return client;
  }
}

Very simple. Now I want to test its behavior when getHttpClient() throws an exception. However, I can’t mock this method, since it is private. What is a common practice in such a situation?

Answer 1

I would make the HTTPClient a field of the class that is set up on construction (via a interface). Then you have the ability to create a mock HTTPClient that can throw an exception during the test if you want, e.g.:

public class Downloader {
  private IHTTPClient client;

  public Downloader(IHTTPClient client) {
    this.client = client;
  }

  public String download(String uri) { 
    this.initialiseHttpClient(); 
    client.setURI(uri); 
    return client.get(); 
  } 

  private HttpClient initialiseHttpClient() { 
    // + some config 
  } 
}

Then call the constructor with a real HTTPClient in production code and a Mock in the test code. You may need to create a wrapper for HTTPClient for the real code.