How do you test code that uses NumberFormat/DecimalFormat?

import java.text.DecimalFormat;
import java.text.NumberFormat;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;

public class NumberFormatTest {

    @Test
    public void testNumberFormat() {
        NumberFormat nf = NumberFormat.getInstance();
        String formatted = nf.format(1234567.89);
        assertEquals("1,234,567.89", formatted);
    }

    @Test
    public void testDecimalFormat() {
        DecimalFormat df = new DecimalFormat("#,##0.00");
        String formatted = df.format(1234567.89);
        assertEquals("1,234,567.89", formatted);
    }
}