*/

  /**
   * Ensures that an object reference passed as a parameter to the calling method is not null.
   *
   * @param reference an object reference
   * @return the non-null reference that was validated
   * @throws NullPointerException if {@code reference} is null
   * @see Verify#verifyNotNull Verify.verifyNotNull()
   */
  @CanIgnoreReturnValue
  public static <T> T checkNotNull(@Nullable T reference) {

    filesystem.setFaultyDelete(cacheDir, false)
    val snapshot = cache["k1"]
    assertThat(snapshot).isNull()
  }

  @ParameterizedTest
  @ArgumentsSource(FileSystemParamProvider::class)
  fun validateKey(parameters: Pair<FileSystem, Boolean>) {
    setUp(parameters.first, parameters.second)
    var key = ""
    assertFailsWith<IllegalArgumentException> {
      key = "has_space "
      cache.edit(key)