assertThat(union(emptySet(), emptySet()).immutableCopy()).isEmpty();
    assertThat(intersection(newHashSet(1, 2), newHashSet(3, 4)).immutableCopy()).isEmpty();
    assertThat(difference(newHashSet(1, 2), newHashSet(1, 2)).immutableCopy()).isEmpty();
    assertThat(symmetricDifference(newHashSet(1, 2), newHashSet(1, 2)).immutableCopy()).isEmpty();
  }

  public void testImmutableCopy() {

            final long took) {
        this.numberOfSuggestDocs = numberOfSuggestDocs;
        this.numberOfInputDocs = numberOfInputDocs;
        this.took = took;
        if (errors == null || errors.isEmpty()) {
            hasError = false;
        } else {
            hasError = true;
            errors.forEach(this.errors::add);
        }
    }

    /**
     * Returns the number of suggest documents.

        if (config.getChildCount() > 0) {
            return true;
        }

        String strValue = config.getValue();

        if (strValue == null || strValue.isEmpty()) {
            return false;
        }

        if (isIgnoredProperty(strValue)) {
            return false;
        }

        // for declaration like @Parameter( property = "config.property" )

                Dependency target, Dependency source, boolean sourceDominant, Map<Object, Object> context) {
            List<Exclusion> tgt = target.getExclusions();
            if (tgt.isEmpty()) {
                List<Exclusion> src = source.getExclusions();

                for (Exclusion element : src) {
                    Exclusion clone = element.clone();
                    target.addExclusion(clone);

        SimpleProblemCollector problems = new SimpleProblemCollector();
        List<Profile> active = selector.getActiveProfiles(profiles, context, problems);
        assertTrue(
                active.isEmpty(), "Expected collection to be empty but had " + active.size() + " elements: " + active);
        assertEquals(1, problems.getErrors().size());
        assertEquals(

                .filter(a -> a.getVersion().startsWith("3."))
                .map(a -> a.getGroupId() + ":" + a.getArtifactId() + ":" + a.getVersion())
                .collect(Collectors.toSet());

        if (!mavenArtifacts.isEmpty()) {
            pluginValidationManager.reportPluginValidationIssue(
                    PluginValidationManager.IssueLocality.EXTERNAL,
                    session,
                    pluginArtifact,

        multimap.asMap().entrySet(), immutableEntry(sampleKey, sampleValueAsCollection));

    // Test #values()

    assertMultimapRemainsUnmodified(multimap, originalEntries);
    if (!multimap.isEmpty()) {
      Collection<V> values = multimap.asMap().entrySet().iterator().next().getValue();

      assertCollectionIsUnmodifiable(values, sampleValue);
    }

    // Test #entries()

        StringBuilder buff = new StringBuilder();
        if (md.getExecutePhase() != null && !md.getExecutePhase().isEmpty()) {
            // forked phase
            if (md.getExecuteLifecycle() != null && !md.getExecuteLifecycle().isEmpty()) {
                buff.append('[');
                buff.append(md.getExecuteLifecycle());
                buff.append(']');
            }

    }

    /**
     * Checks if there are any failures recorded.
     *
     * @return true if there is at least one failure, false otherwise
     */
    public boolean hasFailure() {
        return !failures.isEmpty();
    }

    /**
     * Returns the list of failures.
     *
     * @return a List of Throwable objects representing the failures
     */
    public List<Throwable> getFailures() {
        return failures;

        messages.add(message);
    }

    @Override
    public String toString() {
        return render("");
    }

    public String render(String indentation) {
        if (messages.isEmpty()) {
            return indentation + "There were no validation errors.";
        }

        StringBuilder message = new StringBuilder();
        for (int i = 0; i < messages.size(); i++) {