I have been debugging some existing code for which unit tests are failing on my system, but not on colleagues' systems. The root cause is that SimpleDateFormat is throwing ParseExceptions when parsing dates that should be parseable. I created a unit test that demonstrates the code that is failing on my system:

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;

import junit.framework.TestCase;

public class FormatsTest extends TestCase {

    public void testParse() throws ParseException {
        DateFormat formatter = new SimpleDateFormat("yyyyMMddHHmmss.SSS Z");
        formatter.setTimeZone(TimeZone.getDefault());
        formatter.setLenient(false);

        formatter.parse(formatter.format(new Date()));
    }
}

This test throws a ParseException on my system, but runs successfully on other systems.

java.text.ParseException: Unparseable date: "20100603100243.118 -0600"
    at java.text.DateFormat.parse(DateFormat.java:352)
    at FormatsTest.testParse(FormatsTest.java:16)

I have found that I can setLenient(true) and the test will succeed. The setLenient(false) is what is used in the production code that this test mimics, so I don't want to change it.