// subtracting two ways works
GDuration diff = gd.subtract(gd2);
GDurationBuilder gdb = new GDurationBuilder(gd2);
gdb.setSign(-gdb.getSign());
gdb.addGDuration(gd);
GDuration sum2 = gdb.toGDuration();
Assert.assertEquals(0, diff.compareToGDuration(sum2));
gdb.normalize();
GDurationBuilder gdb1 = new GDurationBuilder(diff);
gdb1.normalize();