@Test
void travel_time_should_be_distance_divided_by_speed() {

    AirDistanceRouter router = new AirDistanceRouter();
    Coordinates from = Coordinates.valueOf(0, 0);
    Coordinates to = Coordinates.valueOf(3, 4); // √(3² + 4²) = 5
    long travelTimeMillis = router.travelTimeMillis(from, to);
    assertThat(travelTimeMillis).isEqualTo((long) (5
            * AirDistanceRouter.KILOMETERS_PER_DEGREE
            / AirDistanceRouter.TRAVEL_SPEED_KPH
            * AirDistanceRouter.MILLIS_IN_ONE_HOUR));
}