@Override
  public List<String> readMultiParam(String key) {
    String[] values = source.getParameterValues(key);
    return values == null ? emptyList() : ImmutableList.copyOf(values);
  }
@Test
  public void read_multi_param_from_source_with_one_value() {
    when(source.getParameterValues("param")).thenReturn(new String[]{"firstValue"});

    List<String> result = underTest.readMultiParam("param");

    assertThat(result).containsExactly("firstValue");
  }