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 ignore milliseconds (or any precision I would like it set to)?

Example of a failing assert that I would like to pass:

Date dateOne = new Date();
dateOne.setTime(61202516585000L);
Date dateTwo = new Date();
dateTwo.setTime(61202516585123L);
assertEquals(dateOne, dateTwo);

Answer 1

Use a DateFormat object with a format that shows only the parts you want to match and do an assertEquals() on the resulting Strings. You can also easily wrap that in your own assertDatesAlmostEqual() method.

Answer 2

I don't know if there is support in JUnit, but one way to do it:

import java.text.SimpleDateFormat;
import java.util.Date;

public class Example {

    private static SimpleDateFormat formatter = new SimpleDateFormat("dd MMM yyyy HH:mm:ss");

    private static boolean assertEqualDates(Date date1, Date date2) {
        String d1 = formatter.format(date1);            
        String d2 = formatter.format(date2);            
        return d1.equals(d2);
    }    

    public static void main(String[] args) {
        Date date1 = new Date();
        Date date2 = new Date();

        if (assertEqualDates(date1,date2)) { System.out.println("true!"); }
    }
}

Answer 3

You could do something like this:

assertTrue((date1.getTime()/1000) == (date2.getTime()/1000));

No String comparisons needed.

Answer 4

Yet another workaround, I'd do it like this:

assertTrue("Dates aren't close enough to each other!", (date2.getTime() - date1.getTime()) < 1000);

Answer 5

If you have Apache commons-lang on your classpath, you can use DateUtils.truncate to round the dates to [some field][3].

assertEquals(DateUtils.truncate(date1,Calendar.SECOND),DateUtils.truncate(date2,Calendar.SECOND));

Answer 6

This is actually a harder problem than it appears because of the boundary cases where the variance that you don't care about crosses a threshold for a value you are checking. e.g. the millisecond difference is less than a second but the two timestamps cross the second threshold, or the minute threshold, or the hour threshold. This makes any DateFormat approach inherently error-prone.

Instead, I would suggest comparing the actual millisecond timestamps and provide a variance delta indicating what you consider an acceptable difference between the two date objects. An overly verbose example follows:

public static void assertDateSimilar(Date expected, Date actual, long allowableVariance)
{
    long variance = Math.abs(allowableVariance);

    long millis = expected.getTime();
    long lowerBound = millis - allowableVariance;
    long upperBound = millis + allowableVariance;

    DateFormat df = DateFormat.getDateTimeInstance();

    boolean within = lowerBound <= actual.getTime() && actual.getTime() <= upperBound;
    assertTrue(MessageFormat.format("Expected {0} with variance of {1} but received {2}", df.format(expected), allowableVariance, df.format(actual)), within);
}

Answer 7

Something like this might work:

assertEquals(new SimpleDateFormat("dd MMM yyyy").format(dateOne), new SimpleDateFormat("dd MMM yyyy").format(dateTwo));