public void set(Map<String, FileHashesDto> previousFileHashesByUuid) {
    checkState(this.previousFileHashesByUuid == null, "Repository already initialized");
    checkNotNull(previousFileHashesByUuid);
    this.previousFileHashesByUuid = Collections.unmodifiableMap(previousFileHashesByUuid);
  }
@Test
  public void fail_if_set_twice() {
    Map<String, FileHashesDto> empty = emptyMap();
    previousFileHashesRepository.set(empty);
    assertThatThrownBy(() -> previousFileHashesRepository.set(empty)).isInstanceOf(IllegalStateException.class);

  }