return Sets.union(Sets.<String>newHashSet(), newHashSet(elements));
                  }
                })
            .named("empty U set")
            .withFeatures(
                CollectionSize.ONE, CollectionSize.SEVERAL, CollectionFeature.ALLOWS_NULL_VALUES)
            .createTestSuite());

    suite.addTest(
        SetTestSuiteBuilder.using(
                new TestStringSetGenerator() {

import static com.google.common.collect.testing.Helpers.copyToList;
import static com.google.common.collect.testing.features.CollectionSize.ONE;
import static com.google.common.collect.testing.features.CollectionSize.SEVERAL;
import static com.google.common.collect.testing.features.CollectionSize.ZERO;
import static com.google.common.collect.testing.testers.ReflectionFreeAssertThrows.assertThrows;
import static java.util.Collections.sort;

 */

package com.google.common.collect.testing.testers;

import static com.google.common.collect.testing.Helpers.getMethod;
import static com.google.common.collect.testing.features.CollectionSize.ONE;
import static com.google.common.collect.testing.features.CollectionSize.ZERO;
import static com.google.common.collect.testing.features.MapFeature.ALLOWS_NULL_KEYS;
import static com.google.common.collect.testing.features.MapFeature.ALLOWS_NULL_VALUES;

    // Split out all the specified sizes.
    Set<Feature<?>> sizesToTest = Helpers.<Feature<?>>copyToSet(CollectionSize.values());
    sizesToTest.retainAll(features);
    features.removeAll(sizesToTest);

    addImpliedFeatures(sizesToTest);
    sizesToTest.retainAll(asList(CollectionSize.ZERO, CollectionSize.ONE, CollectionSize.SEVERAL));

    logger.fine("   Sizes: " + formatFeatureSet(sizesToTest));

    if (sizesToTest.isEmpty()) {

import static com.google.common.collect.testing.Helpers.copyToList;
import static com.google.common.collect.testing.features.CollectionSize.ONE;
import static com.google.common.collect.testing.features.CollectionSize.SEVERAL;
import static com.google.common.collect.testing.features.CollectionSize.ZERO;
import static com.google.common.collect.testing.features.MapFeature.SUPPORTS_REMOVE;
import static java.util.Collections.sort;

import static java.util.Collections.unmodifiableSet;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.collect.testing.features.CollectionFeature;
import com.google.common.collect.testing.features.CollectionSize;
import com.google.common.collect.testing.features.SetFeature;
import java.io.Serializable;
import java.lang.reflect.Method;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Collections;

import static com.google.common.collect.testing.features.CollectionFeature.SUPPORTS_REMOVE;
import static com.google.common.collect.testing.features.CollectionSize.ONE;
import static com.google.common.collect.testing.features.CollectionSize.SEVERAL;
import static com.google.common.collect.testing.features.CollectionSize.ZERO;
import static com.google.common.collect.testing.google.ReflectionFreeAssertThrows.assertThrows;
import static java.util.Arrays.asList;

 * limitations under the License.
 */

package com.google.common.collect.testing.testers;

import static com.google.common.collect.testing.features.CollectionSize.SEVERAL;
import static com.google.common.collect.testing.features.CollectionSize.ZERO;
import static com.google.common.collect.testing.features.MapFeature.FAILS_FAST_ON_CONCURRENT_MODIFICATION;

import static com.google.common.collect.testing.features.CollectionFeature.SUPPORTS_REMOVE;
import static com.google.common.collect.testing.features.CollectionSize.ONE;
import static com.google.common.collect.testing.features.CollectionSize.SEVERAL;
import static com.google.common.collect.testing.features.CollectionSize.ZERO;
import static com.google.common.collect.testing.testers.ReflectionFreeAssertThrows.assertThrows;

import static com.google.common.collect.testing.features.CollectionSize.ONE;
import static com.google.common.collect.testing.features.CollectionSize.SEVERAL;
import static com.google.common.collect.testing.features.CollectionSize.ZERO;

import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.testing.features.CollectionFeature;
import com.google.common.collect.testing.features.CollectionSize;
import org.junit.Ignore;

/**