@Test
void testConvertWorkingDaysToDaysForKarFreitag() {

  Instant gruenDonnerstag2018 = Instant.parse("2018-03-29T01:00:00.000Z");
  Instant days = converter.addWorkingDaysToInstant(gruenDonnerstag2018, Duration.ofDays(0));
  assertThat(days).isEqualTo(gruenDonnerstag2018.plus(0, ChronoUnit.DAYS));
  days = converter.addWorkingDaysToInstant(gruenDonnerstag2018, Duration.ofDays(1)); // Karfreitag
  assertThat(days).isEqualTo(gruenDonnerstag2018.plus(5, ChronoUnit.DAYS)); // osterdienstag
  days = converter.addWorkingDaysToInstant(gruenDonnerstag2018, Duration.ofDays(2)); // Karfreitag
  assertThat(days).isEqualTo(gruenDonnerstag2018.plus(6, ChronoUnit.DAYS)); // ostermittwoch
}