assertThrows(
        IllegalArgumentException.class,
        () -> COMMA_SPLITTER.withKeyValueSeparator(":").split("a:1,b:2,a:3"));
  }

  public void testMapSplitter_varyingTrimLevels() {
    MapSplitter splitter = COMMA_SPLITTER.trimResults().withKeyValueSeparator(Splitter.on("->"));
    Map<String, String> split = splitter.split(" x -> y, z-> a ");
    assertThat(split).containsEntry("x ", " y");