SUPPORTS_REMOVE,
  FAILS_FAST_ON_CONCURRENT_MODIFICATION,
  /**
   * Indicates that the constructor or factory method of a map, usually an immutable map, throws an
   * {@link IllegalArgumentException} when presented with duplicate keys instead of discarding all
   * but one.
   */
  REJECTS_DUPLICATES_AT_CREATION,

  GENERAL_PURPOSE(SUPPORTS_PUT, SUPPORTS_REMOVE);

  private final Set<Feature<? super Map>> implied;

@SuppressWarnings("JUnit4ClassUsedInJUnit3")
public class SetMultimapPutTester<K, V> extends AbstractMultimapTester<K, V, SetMultimap<K, V>> {
  // Tests for non-duplicate values are in MultimapPutTester

  @MapFeature.Require(SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPutDuplicateValuePreservesSize() {
    assertFalse(multimap().put(k0(), v0()));

 * elements.
 *
 * <p>The collections created by {@link #createCollection()} may or may not allow duplicates. If the
 * collection, such as a {@link Set}, does not support duplicates, an added key-value pair will
 * replace an existing pair with the same key and value, if such a pair is present. With collections
 * like {@link List} that allow duplicates, the collection will keep the existing key-value pairs
 * while adding a new pair.
 *

@SuppressWarnings("JUnit4ClassUsedInJUnit3")
public class ListMultimapPutTester<K, V> extends AbstractListMultimapTester<K, V> {
  // MultimapPutTester tests non-duplicate values, but ignores ordering

  @MapFeature.Require(SUPPORTS_PUT)
  public void testPutAddsValueAtEnd() {
    for (K key : sampleKeys()) {
      for (V value : sampleValues()) {
        resetContainer();

            requireNonNull(type, "type");
            requireNonNull(component, "component");
            if (components.put(type, component) != null) {
                throw new IllegalStateException("Duplicate mapping for type: " + type.getName());
            }
            return this;
        }
    }

            return None

    def _create_credentials_fetcher(self):
        method = self.METHOD

        def fetch_credentials():
            # HTTP headers are case insensitive filter out
            # all duplicate headers and pick one.
            headers = {}
            headers['content-type'] = 'application/x-www-form-urlencoded'
            headers['authorization'] = urllib3.make_headers(

  public void testLastIndexOf_duplicate() {
    E[] array = createSamplesArray();
    array[getNumElements() / 2] = e0();
    collection = getSubjectGenerator().create(array);
    assertEquals(
        "lastIndexOf(duplicate) should return index of last occurrence",
        getNumElements() / 2,
        getList().lastIndexOf(e0()));
  }

* `frozenset`:
    * In requests and responses, treated the same as a `set`:
        * In requests, a list will be read, eliminating duplicates and converting it to a `set`.
        * In responses, the `set` will be converted to a `list`.
        * The generated schema will specify that the `set` values are unique (using JSON Schema's `uniqueItems`).
* `bytes`:

import java.util.Map.Entry;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Set;
import org.jspecify.annotations.Nullable;

/**
 * Implementation of {@code Multimap} that does not allow duplicate key-value entries and that
 * returns collections whose iterators follow the ordering in which the data was added to the
 * multimap.
 *

import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;
import org.jspecify.annotations.Nullable;

/**
 * Implementation of {@code Multimap} that does not allow duplicate key-value entries and that
 * returns collections whose iterators follow the ordering in which the data was added to the
 * multimap.
 *