assertMapEquals(zis.combine(zat).build(), "one", 1, "two", 2, "three", 3);
  }

  // TODO(b/172823566): Use mainline testToImmutableMap once CollectorTester is usable to java7.
  public void testToImmutableMap_exceptionOnDuplicateKey_java7_combine() {
    ImmutableMap.Builder<String, Integer> zis =
        ImmutableMap.<String, Integer>builder().put("one", 1).put("two", 2);
    ImmutableMap.Builder<String, Integer> zat =