public static Map<String, String> loadProperties(final File propertiesFile) {
    return loadProperties(ImmutableList.of(propertiesFile));
  }
@Test
  public void shouldLoadImmutablePropsFromFile() {
    // Given:
    givenPropsFileContains(
        "some.prop=some value" + System.lineSeparator()
    );

    final Map<String, String> result = PropertiesUtil.loadProperties(propsFile);

    // When
    assertThrows(
        UnsupportedOperationException.class,
        () -> result.put("new", "value")
    );
  }