How to mock new Date() in java using Mockito

Question

I have a function that uses the current time to make some calculations. I\'d like to mock it using mockito.

An example of the class I\'d like to test:

Answer 1

Date now = new Date();    
now.set(2018, Calendar.FEBRUARY, 15, 1, 0); // set date to 2018-02-15
//set current time to 2018-02-15
mockCurrentTime(now.getTimeInMillis());

private void mockCurrentTime(long currTimeUTC) throws Exception {
    // mock new dates with current time
    PowerMockito.mockStatic(Date.class);
    PowerMockito.whenNew(Date.class).withNoArguments().thenAnswer(new Answer() {

        @Override
        public Date answer(InvocationOnMock invocation) throws Throwable {
            return new Date(currTimeUTC);
        }
    });

    //do not mock creation of specific dates
    PowerMockito.whenNew(Date.class).withArguments(anyLong()).thenAnswer(new Answer() {

        @Override
        public Date answer(InvocationOnMock invocation) throws Throwable {
            return new Date((long) invocation.getArguments()[0]);
        }
    });

    // mock new calendars created with time zone
    PowerMockito.mockStatic(Calendar.class);
    Mockito.when(Calendar.getInstance(any(TimeZone.class))).thenAnswer(new Answer() {
        @Override
        public Calendar answer(InvocationOnMock invocation) throws Throwable {
            TimeZone tz = invocation.getArgumentAt(0, TimeZone.class);
            Calendar cal = Calendar.getInstance(tz);
            cal.setTimeInMillis(currTimeUTC);
            return cal;
        }
    });
}