public Frequency add(Frequency value) {
        return new Frequency(this.frequency + value.frequency);
    }
@Test
    public void testAdd() {
        Frequency low = Frequency.ofMHz(100);
        Frequency high = Frequency.ofGHz(1);
        Frequency expected = Frequency.ofMHz(1100);

        assertThat(low.add(high), is(expected));
    }