DateSubject - custom Truth extension subject for comparing Dates

DateSubject.java

import com.google.common.truth.FailureStrategy;
import com.google.common.truth.Subject;
import com.google.common.truth.SubjectFactory;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;

import static com.google.common.truth.Truth.assert_;

public class DateSubject
      extends Subject<DateSubject, Date> {

    private static final SubjectFactory<DateSubject, Date> FACTORY = new SubjectFactory<DateSubject, Date>() {
        @Override
        public DateSubject getSubject(FailureStrategy fs, Date target) {
            return new DateSubject(fs, target);
        }
    };

    private DateSubject(FailureStrategy failureStrategy, Date subject) {
        super(failureStrategy, subject);
    }

    /**
     * Use this for a convenient API call like so:
     * DateSubject.assertThat(date1).isTheSameDay(date2);
     */
    public static DateSubject assertThat(Date testDate) {
        return assert_().about(date()).that(testDate);
    }

    public DateSubject isTheSameDay(Date date) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd", Locale.getDefault());

        String dateString1 = sdf.format(getSubject());
        String dateString2 = sdf.format(date);
        if (!dateString1.equalsIgnoreCase(dateString2)) {
            fail(String.format(Locale.getDefault(),
                               "date's don't appear to be the same \n[%s]\n[%s]",
                               dateString1,
                               dateString2));
        }
        return this;
    }

    public DateSubject isNotTheSameDay(Date date) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd", Locale.getDefault());

        String dateString1 = sdf.format(getSubject());
        String dateString2 = sdf.format(date);
        if (dateString1.equalsIgnoreCase(dateString2)) {
            fail(String.format(Locale.getDefault(),
                               "date's appear to be the same \n[%s]\n[%s]",
                               dateString1,
                               dateString2));
        }
        return this;
    }

    static SubjectFactory<DateSubject, Date> date() {
        return FACTORY;
    }
}