import static com.google.common.collect.Lists.newArrayList;
import static com.google.common.collect.Lists.transform;
import static com.google.common.collect.Maps.immutableEntry;
import static com.google.common.collect.Multimaps.synchronizedMultimap;
import static com.google.common.collect.ReflectionFreeAssertThrows.assertThrows;
import static com.google.common.collect.Sets.newHashSet;
import static com.google.common.collect.testing.Helpers.mapEntry;

import static com.google.common.collect.Multimaps.filterKeys;
import static com.google.common.collect.Multimaps.synchronizedListMultimap;
import static com.google.common.collect.Multimaps.synchronizedMultimap;
import static com.google.common.collect.Multimaps.synchronizedSetMultimap;
import static com.google.common.collect.Multimaps.synchronizedSortedSetMultimap;

 * underlying map and {@link #createCollection()} method return threadsafe classes. Concurrent read
 * operations will work correctly. To allow concurrent update operations, wrap your multimap with a
 * call to {@link Multimaps#synchronizedMultimap}.
 *
 * <p>For serialization to work, the subclass must specify explicit {@code readObject} and {@code
 * writeObject} methods.
 *
 * @author Jared Levy
 * @author Louis Wasserman
 */
@GwtCompatible