* conformance of concrete {@link Map} subclasses to that contract.
 *
 * @param <K> the type of keys used by the maps under test
 * @param <V> the type of mapped values used the maps under test
 * @author George van den Driessche
 */
// TODO: Descriptive assertion messages, with hints as to probable fixes.

    return CollectCollectors.toImmutableSetMultimap(keyFunction, valueFunction);
  }

  /**
   * Returns a {@code Collector} accumulating entries into an {@code ImmutableSetMultimap}. Each
   * input element is mapped to a key and a stream of values, each of which are put into the
   * resulting {@code Multimap}, in the encounter order of the stream and the encounter order of the
   * streams of values.
   *
   * <p>Example:
   *

   *
   * <p>When there are multiple instances of a key in this iterable, it is unspecified whether
   * {@code valueFunction} will be applied to more than one instance of that key and, if it is,
   * which result will be mapped to that key in the returned map.
   *
   * <p><b>{@code Stream} equivalent:</b> use {@code stream.collect(ImmutableMap.toImmutableMap(k ->

   * inputs, with counts equal to the result of applying {@code countFunction} to the inputs.
   * Elements are added in encounter order.
   *
   * <p>If the mapped elements contain duplicates (according to {@link Object#equals}), the element
   * will be added more than once, with the count summed over all appearances of the element.
   *

   * inputs, with counts equal to the result of applying {@code countFunction} to the inputs.
   * Elements are added in encounter order.
   *
   * <p>If the mapped elements contain duplicates (according to {@link Object#equals}), the element
   * will be added more than once, with the count summed over all appearances of the element.
   *

   * keys and values are the result of applying the provided mapping functions to the input
   * elements. The generated map is sorted by the specified comparator.
   *
   * <p>If the mapped keys contain duplicates (according to the specified comparator), an {@code
   * IllegalArgumentException} is thrown when the collection operation is performed. (This differs

   * resulting implementation is specialized for enum key types. The returned map and its views will
   * iterate over keys in their enum definition order, not encounter order.
   *
   * <p>If the mapped keys contain duplicates, an {@code IllegalArgumentException} is thrown when
   * the collection operation is performed. (This differs from the {@code Collector} returned by

   * resulting implementation is specialized for enum key types. The returned map and its views will
   * iterate over keys in their enum definition order, not encounter order.
   *
   * <p>If the mapped keys contain duplicates, an {@code IllegalArgumentException} is thrown when
   * the collection operation is performed. (This differs from the {@code Collector} returned by

    return CollectCollectors.toImmutableSetMultimap(keyFunction, valueFunction);
  }

  /**
   * Returns a {@code Collector} accumulating entries into an {@code ImmutableSetMultimap}. Each
   * input element is mapped to a key and a stream of values, each of which are put into the
   * resulting {@code Multimap}, in the encounter order of the stream and the encounter order of the
   * streams of values.
   *
   * <p>Example:
   *

   * and values are the result of applying the provided mapping functions to the input elements.
   * Entries appear in the result {@code ImmutableBiMap} in encounter order.
   *
   * <p>If the mapped keys or values contain duplicates (according to {@link
   * Object#equals(Object)}), an {@code IllegalArgumentException} is thrown when the collection