File file = root();
    assertThat(file.getParentFile()).isNull();
    assertThat(file.getCanonicalFile().getParentFile()).isNull();
    Files.createParentDirs(file);
  }

  public void testCreateParentDirs_relativePath() throws IOException {
    File file = file("nonexistent.file");
    assertThat(file.getParentFile()).isNull();
    assertThat(file.getCanonicalFile().getParentFile()).isNotNull();