Question

I have an error condition that I want to test. The behavior I want to verify is that an error message gets written to the log. Since Mockito can’t stub static methods, this is rather difficult, because I want my class-under-test to either write directly to System.err.println() or my static Log.error() method. I don’t want to have to inject a mocked “logger object” into every single object that might write error messages!

So I guess what I’m asking is, what do you think is the best way to structure my Log class and/or the class-under-test so that I can stub out the logging methods or replace them with a mocked logger?

The best answer might not even make use of Mockito, it could be anything. I’d rather not import yet another library like PowerMock, but if you have a good answer that requires something like that I wouldn’t mind seeing it.

Answer 1

If you want to keep your logging logic in static methods, you can still initialize real logging implementation when the class is loaded based on some system property:

class Log {

  private static MyLogger logger;

  static {
    String className = System.getProperty("my.static.logger.class.name");
    // Instantiate your logger here...
    // By default use some DefaultLogger implementation...
  }

  public static void error(String message, Throwable t) {
    logger.error(message, t);
  }

}

Then when you run your test you can specify a mock class name using -D property. But you will need to implement your mock logging class without mockito magic.