Question

I use JodaTime#DateTime, and I need to mock its behavior. Since it is not possible to directly mock JodaTime#DateTime, I create an interface of it

Clock.java

public interface Clock {
    DateTime getCurrentDateTimeEST();
    DateTime getFourPM_EST();
    DateTime getSevenPM_EST();
}

JodaTime.java

public class JodaTime implements Clock {

    @Override
    public DateTime getCurrentDateTimeEST() {
        return new DateTime(DateTimeZone.forID("EST"));
    }

    @Override
    public DateTime getFourPM_EST() {
        DateTime current = getCurrentDateTimeEST();
        return new DateTime(current.getYear(), current.getMonthOfYear(), 
                current.getDayOfMonth(), 16, 0, 0, 0, DateTimeZone.forID("EST"));
    }

    @Override
    public DateTime getSevenPM_EST() {
        DateTime current = getCurrentDateTimeEST();
        return new DateTime(current.getYear(), current.getMonthOfYear(), 
                current.getDayOfMonth(), 19, 0, 0, 0, DateTimeZone.forID("EST")); 
    }   
}

Here is the method that I want to test

public class PrintProcessor{

  Clock jodaTime;

  public PrintProcessor(){
      jodaTime = new JodaTime();
  }
  ...
  public String getPrintJobName(Shipper shipper){
    String printJobName = null;
    //Get current EST time
    if(jodaTime.getCurrentDateTimeEST().isBefore(jodaTime.getFourPM_EST()) ||
            jodaTime.getCurrentDateTimeEST().isAfter(jodaTime.getSevenPM_EST())){   //Before 4PM EST and after 7PM EST
        switch(shipper){
        case X:
        ...
    }else if(jodaTime.getCurrentDateTimeEST().isBefore(jodaTime.getSevenPM_EST())){ //Between 4PM-7PM EST
        switch(shipper){
        case X:
        ... 
    }
    return printJobName;
  }
}

As you can see the printJobName depend on the current time of the day relative to the time interval [4PM-7PM] EST and the Shipper name. Since Shipper will be pass via parameter, we can unit test it no problem. But I need to mock the time. So here is what I try

@Test
public void testGetPrintJobNameBeforeFourPM(){
    DateTime current = new DateTime(DateTimeZone.forID("EST"));
    Clock clock = mock(Clock.class);
    //Always return 6pm when I try to ask for the current time
    when(clock.getCurrentDateTimeEST()).thenReturn(new DateTime(current.getYear(), current.getMonthOfYear(), 
            current.getDayOfMonth(), 18, 0, 0, 0, DateTimeZone.forID("EST")));
    //Test for Fedex
    String printJobName = printProcessor.getPrintJobName(Shipper.X);
    assertEquals("XNCRMNCF", printJobName);
}

The test should fail since I pass in 6PM, but XNCRMNCF is the name for before 4PM. Do I need to mock printProcessor as well. If what I have is wrong. How should I fix it? I am trying to learn writing high level java code, please be very criticized about my code. I really want to learn

Answer 1

This is a classic case of testing showing up a potential flaw in design. You cannot mock JodaTime because you have a hard-wired dependency to these classes in your class-under-test.

Have a look at the SOLID principles to understand why this could be a problem (especially in this case the Dependency Inversion Principle). If you injected JodaTime somewhere as a dependency, then in your unit test you would be able to replace a real instace of it with a mock, stub or spy as appropriate.

However: JodaTime is something that is highly unlikely to be injected with anything else in the production environment, no matter how long it is live for. Instead, in this case you would probably be better served with the Composed Method Design Pattern. Here, you would extract whatever calculation/algorithm you use to generate the printjobName to another method (I can’t see how you do it here because your code snippet never assigns a value to that variable). Then you can spy (partial mock) your class under test to only mock that method and return a fixed value, regardless of the real date time that JodaTime is delivering, for instance:

public class PrintProcessor {
    ...
    public String getPrintJobName(Shipper shipper) {
        String printJobName = null;
        String timeHash = this.getTimeHash();
        if (this.isBeforeFourPM()) {
            switch(shipper) {
                printJobName = // Do something with timeHash to generate name
            }
        } else {
            ...
        }
        return printJobName;
    }

    public boolean isBeforeFourPM() {
        return (jodaTime.getCurrentDateTimeEST().isBefore(jodaTime.getFourPM_EST()) ||
            jodaTime.getCurrentDateTimeEST().isAfter(jodaTime.getSevenPM_EST()));
    }

    public String getTimeHash() {
        ... // Do something to hash the time value in to a String
    }
}

Now you can write in your test:

@Test
public void testGetPrintJobNameBeforeFourPM() {
    PrintProcessor concretePrintProcessor = new PrintProcessor();
    PrintProcessor printProcessor = spy(concretePrintProcessor);
    doReturn(true).when(printProcessor).isBeforeFourPM();

    String printJobName = printProcessor.getPrintJobName(Shipper.X);

    assertEquals("XNCRMNCF", printJobName);
}