Compare Date objects with different levels of precision

Question

I have a JUnit test that fails because the milliseconds are different. In this case I don\'t care about the milliseconds. How can I change the precision of the assert to i

Answer 1

Instead of using new Date directly, you can create a small collaborator, which you can mock out in your test:

public class DateBuilder {
    public java.util.Date now() {
        return new java.util.Date();
    }
}

Create a DateBuilder member and change calls from new Date to dateBuilder.now()

import java.util.Date;

public class Demo {

    DateBuilder dateBuilder = new DateBuilder();

    public void run() throws InterruptedException {
        Date dateOne = dateBuilder.now();
        Thread.sleep(10);
        Date dateTwo = dateBuilder.now();
        System.out.println("Dates are the same: " + dateOne.equals(dateTwo));
    }

    public static void main(String[] args) throws InterruptedException {
        new Demo().run();
    }
}

The main method will produce:

Dates are the same: false

In the test you can inject a stub of DateBuilder and let it return any value you like. For example with Mockito or an anonymous class which overrides now():

public class DemoTest {

    @org.junit.Test
    public void testMockito() throws Exception {
        DateBuilder stub = org.mockito.Mockito.mock(DateBuilder.class);
        org.mockito.Mockito.when(stub.now()).thenReturn(new java.util.Date(42));

        Demo demo = new Demo();
        demo.dateBuilder = stub;
        demo.run();
    }

    @org.junit.Test
    public void testAnonymousClass() throws Exception {
        Demo demo = new Demo();
        demo.dateBuilder = new DateBuilder() {
            @Override
            public Date now() {
                return new Date(42);
            }
        };
        demo.run();
    }
}