public File contextProperties() {
    return new File(dir, "context-props.pb");
  }
@Test
  public void contextProperties_file() throws Exception {
    File dir = temp.newFolder();
    File file = new File(dir, "context-props.pb");
    FileUtils.write(file, "content");

    FileStructure structure = new FileStructure(dir);
    assertThat(structure.contextProperties()).exists().isFile().isEqualTo(file);
  }