{
      Collector<Cell<String, String, Integer>, ?, ImmutableTable<String, String, Integer>>
          collector = toImmutableTable(Cell::getRowKey, Cell::getColumnKey, t -> null);
      assertThrows(
          NullPointerException.class,
          () -> Stream.of(immutableCell("one", "uno", 1)).collect(collector));
    }
    {

  @SuppressWarnings({"rawtypes", "unchecked"})
  static <E> Collector<E, ?, ImmutableList<E>> toImmutableList() {
    return (Collector) TO_IMMUTABLE_LIST;
  }

  // Sets

  @SuppressWarnings({"rawtypes", "unchecked"})
  static <E> Collector<E, ?, ImmutableSet<E>> toImmutableSet() {
    return (Collector) TO_IMMUTABLE_SET;
  }

  static <E> Collector<E, ?, ImmutableSortedSet<E>> toImmutableSortedSet(

  @SuppressWarnings({"rawtypes", "unchecked"})
  static <E> Collector<E, ?, ImmutableList<E>> toImmutableList() {
    return (Collector) TO_IMMUTABLE_LIST;
  }

  // Sets

  @SuppressWarnings({"rawtypes", "unchecked"})
  static <E> Collector<E, ?, ImmutableSet<E>> toImmutableSet() {
    return (Collector) TO_IMMUTABLE_SET;
  }

  static <E> Collector<E, ?, ImmutableSortedSet<E>> toImmutableSortedSet(

        ProblemCollector collector = ProblemCollectorFactory.newInstance(null);
        collector.setSource("pom.xml");
        collector.add(Problem.Severity.ERROR, "Error message", 10, 5, null);
        collector.add(Problem.Severity.WARNING, "Warning message", 15, 3, null);

        List<Problem> problems = collector.getProblems();
        assertEquals(2, problems.size(), "Should collect both problems");

    Collector<Entry<AnEnum, Integer>, ?, ImmutableMap<AnEnum, Integer>> collector =
        toImmutableEnumMap(Entry::getKey, Entry::getValue);
    assertThrows(
        IllegalArgumentException.class,
        () -> Stream.of(mapEntry(AnEnum.A, 1), mapEntry(AnEnum.A, 11)).collect(collector));
  }

  public void testToImmutableMapMerging() {

     */
    @Nonnull
    Stream<P> problems(BuilderProblem.Severity severity);

    /**
     * Creates an "empty" problem collector that doesn't store any problems.
     *
     * @param <P> the type of problem
     * @return an empty problem collector
     */
    @Nonnull
    static <P extends BuilderProblem> ProblemCollector<P> empty() {
        return new ProblemCollector<>() {

import com.google.common.base.Equivalence;
import com.google.common.collect.ImmutableSet.Builder;
import com.google.common.collect.testing.ListTestSuiteBuilder;
import com.google.common.collect.testing.SetTestSuiteBuilder;
import com.google.common.collect.testing.TestStringSetGenerator;
import com.google.common.collect.testing.features.CollectionFeature;
import com.google.common.collect.testing.features.CollectionSize;

    }

    @CanIgnoreReturnValue
    @Override
    public Builder<E> addAll(Iterable<? extends E> elements) {
      if (elements instanceof Collection) {
        Collection<?> collection = (Collection<?>) elements;
        contents.ensureCapacity(contents.size() + collection.size());
      }
      super.addAll(elements);
      return this;
    }

    @CanIgnoreReturnValue
    @Override

        private final OutputStream collector;

        public CacheStream(final OutputStream stream, final OutputStream collector) {
            this.stream = stream;
            this.collector = collector;
        }

        @Override
        public void close() throws IOException {
            stream.close();
            collector.close();
        }

        @Override

import com.google.common.base.Equivalence;
import com.google.common.collect.ImmutableSortedMap.Builder;
import com.google.common.collect.testing.ListTestSuiteBuilder;
import com.google.common.collect.testing.MapTestSuiteBuilder;
import com.google.common.collect.testing.NavigableMapTestSuiteBuilder;
import com.google.common.collect.testing.features.CollectionFeature;
import com.google.common.collect.testing.features.CollectionSize;