@Test
public void with_empty_file() throws IOException {

    URL weatherFile = getResource("empty.dat");
    WeatherFileLineProcessor weatherFileLineProcessor = new WeatherFileLineProcessor();
    WeatherFileReader weatherFileReader = new WeatherFileReader(weatherFile, weatherFileLineProcessor);
    SmallestTemperatureSpread smallestTemperatureSpread = new SmallestTemperatureSpread(weatherFileReader);
    Optional<Integer> minTemperatureSpreadDay = smallestTemperatureSpread.minTemperatureSpreadDay();
    assertThat(minTemperatureSpreadDay).isEmpty();
}