@Test
public void should_find_day_of_the_smallest_temperature_in_extremum_value() throws IOException {

    List<TemperatureExtremum> extrema = newArrayList(
            new TemperatureExtremum(1, 88, 59),
            new TemperatureExtremum(2, 79, 53));
    doReturn(extrema).when(weatherFileReader).readFile();
    Optional<Integer> minTemperaturesSpread = smallestTemperatureSpread.minTemperatureSpreadDay();
    assertThat(minTemperaturesSpread).hasValue(2);
}