+ "a null element in an entry counts as having a hash of zero).",
        expectedHashCode,
        getMap().hashCode());
  }

  private static int hash(Entry<?, ?> e) {
    return (e.getKey() == null ? 0 : e.getKey().hashCode())
        ^ (e.getValue() == null ? 0 : e.getValue().hashCode());
  }

        "putIfAbsent(notPresent, value) should return null", getMap().putIfAbsent(k3(), v3()));
    expectAdded(e3());
  }

  @MapFeature.Require(SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPutIfAbsent_supportedPresent() {
    assertEquals(
        "putIfAbsent(present, value) should return existing value",
        v0(),
        getMap().putIfAbsent(k0(), v3()));
    expectUnchanged();
  }

@SuppressWarnings("JUnit4ClassUsedInJUnit3")
@NullMarked
public class ConcurrentMapPutIfAbsentTester<K, V> extends AbstractMapTester<K, V> {
  @Override
  protected ConcurrentMap<K, V> getMap() {
    return (ConcurrentMap<K, V>) super.getMap();
  }

  @MapFeature.Require(SUPPORTS_PUT)
  public void testPutIfAbsent_supportedAbsent() {
    assertNull("putIfAbsent(notPresent, value) should return null", putIfAbsent(e3()));

    assertEquals(c.getKey(), navigableMap.lastKey());
  }

  @CollectionSize.Require(absent = ZERO)
  public void testHeadMapExclusive() {
    assertFalse(navigableMap.headMap(a.getKey()).containsKey(a.getKey()));
  }

  @CollectionSize.Require(absent = ZERO)
  public void testTailMapInclusive() {
    assertTrue(navigableMap.tailMap(a.getKey()).containsKey(a.getKey()));
  }

  public void testHeadMap() {

  public void testToString_formatting() {
    assertEquals(
        "map.toString() incorrect", expectedToString(getMap().entrySet()), getMap().toString());
  }

  private String expectedToString(Set<Entry<K, V>> entries) {
    Map<K, V> reference = new LinkedHashMap<>();
    for (Entry<K, V> entry : entries) {
      reference.put(entry.getKey(), entry.getValue());
    }
    return reference.toString();
  }

        "putIfAbsent(notPresent, value) should return null", getMap().putIfAbsent(k3(), v3()));
    expectAdded(e3());
  }

  @MapFeature.Require(SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPutIfAbsent_supportedPresent() {
    assertEquals(
        "putIfAbsent(present, value) should return existing value",
        v0(),
        getMap().putIfAbsent(k0(), v3()));
    expectUnchanged();
  }

    @Test
    public void testEntrySet() throws Exception {
        Iterator<Map.Entry<String, String>> i = map.entrySet().iterator();
        assertThat(i.next().getKey(), is(nullValue()));
        assertThat(i.next().getKey(), is("1"));
        assertThat(i.next().getKey(), is("2"));
    }

    /**
     * Test method for {@link org.seasar.util.collection.ArrayIterator#remove()}
     * .
     */
    @Test

    assertNull("put(null, null) should return null", put(nullKeyValueEntry));
    expectAdded(nullKeyValueEntry);
  }

  @CanIgnoreReturnValue
  private V put(Entry<K, V> entry) {
    return getMap().put(entry.getKey(), entry.getValue());
  }

  /**
   * Returns the {@link Method} instance for {@link #testPut_nullKeyUnsupported()} so that tests of
   * {@link java.util.TreeMap} can suppress it with {@code

  public void testPutAll_nullCollectionReference() {
    assertThrows(NullPointerException.class, () -> getMap().putAll(null));
  }

  private void putAll(Iterable<Entry<K, V>> entries) {
    Map<K, V> map = new LinkedHashMap<>();
    for (Entry<K, V> entry : entries) {
      map.put(entry.getKey(), entry.getValue());
    }
    getMap().putAll(map);
  }

  /**

  public void testPutAll_nullCollectionReference() {
    assertThrows(NullPointerException.class, () -> getMap().putAll(null));
  }

  private void putAll(Iterable<Entry<K, V>> entries) {
    Map<K, V> map = new LinkedHashMap<>();
    for (Entry<K, V> entry : entries) {
      map.put(entry.getKey(), entry.getValue());
    }
    getMap().putAll(map);
  }

  /**