private static final ImmutableList<String> STRINGS = ImmutableList.of("123", "456");
  private static final ImmutableList<Long> LONGS = ImmutableList.of(123L, 456L);

  public void testConverter() {
    assertEquals(LONG_VAL, STR_TO_LONG.convert(STR_VAL));
    assertThat(STR_TO_LONG.reverse().convert(LONG_VAL)).isEqualTo(STR_VAL);

    Iterable<Long> convertedValues = STR_TO_LONG.convertAll(STRINGS);