如何使用Mockito模拟静态方法以进行单元测试

Question

I have a method like this.

 public Response post(String json) {

   EventList list = Recorder.getRecorders();
   if (null == list || list.isEmpty()) {
     throw new ServiceUnavailableException("An Recorder is either not configured");
  }
  String targetIUrl = list.getNext().getBase();
  String targetV2Url = targetUrl + "/v2";

 // other processes......
}

1. I want to mock Recorder.getRecorder() and do something like when(Recorder.getRecorder()).thenReturn(null) and test if throw a 503 exception. But getRecorder() is a static method. I know Mockito cannot mock the static method, but I still wanna know if it is possible to change some code made this testable without using Powermock or other libraries.

2. If I mock Recorder, do I have to change the method to post(String json, Recorder recorder)? Otherwise, how can I make this mock interact with the method?

Answer 1

If you want to mock the getRecorders() behaviour without using a library for mocking static methods (such as Powermock) then you'll have to extract the static call from inside post() . There are a few options for this:

1. Pass the EventList into post()

    public post(String json, EventList list) { ... } 

2. Inject the EventList into the class which contains post()

    public class TheOneThatContainsThePostMethod { private EventList eventList; public TheOneThatContainsThePostMethod(EventList eventList) { this.eventList = eventList; } public post(String json) { if (null == this.eventList || this.eventList.isEmpty()) { throw new ServiceUnavailableException("An Recorder is either not configured"); } } } 

3. Hide the static method call inside another class and inject an instance of that class into post() or the class which contains post() . For example:

    public class RecorderFactory { public EventList get() { return Recorder.getRecorders(); } } public class TheOneThatContainsThePostMethod { private RecorderFactory recorderFactory; public TheOneThatContainsThePostMethod(RecorderFactory recorderFactory) { this.recorderFactory = recorderFactory; } public post(String json) { EventList list = recorderFactory.getRecorders(); ... } } // Or ... public post(String json, RecorderFactory recorderFactory) { EventList list = recorderFactory.getRecorders(); ... } 

With the first two approaches your test can simply invoke post() providing (1) a null EventList ; (2) an empty EventList ... thereby allowing you to test the 'throw a 503 exception' behaviour.

With the third approach you can use Mockito to mock the behaviour of the RecorderFactory to return (1) a null EventList ; (2) an empty EventList ... thereby allowing you to test the 'throw a 503 exception' behaviour.