The right thing to do is to restructure your code to make it more testable as shown below.
Restructuring your code to remove the direct dependency on Date will allow you to inject different implementations for normal runtime and test runtime:
interface DateTime {
Date getDate();
}
class DateTimeImpl implements DateTime {
@Override
public Date getDate() {
return new Date();
}
}
class MyClass {
private final DateTime dateTime;
// inject your Mock DateTime when testing other wise inject DateTimeImpl
public MyClass(final DateTime dateTime) {
this.dateTime = dateTime;
}
public long getDoubleTime(){
return dateTime.getDate().getTime()*2;
}
}
public class MyClassTest {
private MyClass myClassTest;
@Before
public void setUp() {
final Date date = Mockito.mock(Date.class);
Mockito.when(date.getTime()).thenReturn(30L);
final DateTime dt = Mockito.mock(DateTime.class);
Mockito.when(dt.getDate()).thenReturn(date);
myClassTest = new MyClass(dt);
}
@Test
public void someTest() {
final long doubleTime = myClassTest.getDoubleTime();
assertEquals(60, doubleTime);
}
}