CollectorTester<T, A, R> of(
          Collector<T, A, R> collector, BiPredicate<? super R, ? super R> equivalence) {
    return new CollectorTester<>(collector, equivalence);
  }

  private final Collector<T, A, R> collector;
  private final BiPredicate<? super R, ? super R> equivalence;

  private CollectorTester(
      Collector<T, A, R> collector, BiPredicate<? super R, ? super R> equivalence) {

  private final BiPredicate<? super R, ? super R> equivalence;

  private CollectorTester(
      Collector<T, A, R> collector, BiPredicate<? super R, ? super R> equivalence) {
    this.collector = checkNotNull(collector);
    this.equivalence = checkNotNull(equivalence);
  }

  /**
   * Different orderings for combining the elements of an input array, which must all produce the
   * same result.
   */

  @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(

                .append(": ")
                .append(problem.getMessage()));
        return msg.toString();
    }

    /**
     * Returns the problem collector associated with this exception.
     *
     * @return the problem collector containing all problems related to this exception
     */
    public ProblemCollector<BuilderProblem> getProblemCollector() {
        return problems;
    }

        context.put("project.baseUri", "myBaseUri");
    }

    protected void assertProblemFree(SimpleProblemCollector collector) {
        assertEquals(0, collector.getErrors().size(), "Expected no errors");
        assertEquals(0, collector.getWarnings().size(), "Expected no warnings");
        assertEquals(0, collector.getFatals().size(), "Expected no fatals");
    }

    @SuppressWarnings("SameParameterValue")

        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");

import org.apache.maven.project.ProjectBuildingResult;
import org.apache.maven.project.collector.DefaultProjectsSelector;
import org.apache.maven.project.collector.MultiModuleCollectionStrategy;
import org.apache.maven.project.collector.PomlessCollectionStrategy;
import org.apache.maven.project.collector.ProjectsSelector;
import org.apache.maven.project.collector.RequestPomCollectionStrategy;
import org.junit.jupiter.api.BeforeEach;

     */
    @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<>() {

    checkNonnegative(k, "k");
    checkNotNull(comparator);
    return Collector.of(
        () -> TopKSelector.<T>least(k, comparator),
        TopKSelector::offer,
        TopKSelector::combine,
        TopKSelector::topK,
        Collector.Characteristics.UNORDERED);
  }

  /**
   * Returns a {@code Collector} that returns the {@code k} greatest (relative to the specified

        private final OutputStream collector;

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

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

        @Override