public void testPutDuplicateValue() {
    List<Entry<K, V>> entries = copyToList(multimap().entries());

    for (Entry<K, V> entry : entries) {
      resetContainer();

      K k = entry.getKey();
      V v = entry.getValue();

      List<V> values = multimap().get(k);
      List<V> expectedValues = copyToList(values);

      assertTrue(multimap().put(k, v));
      expectedValues.add(v);

            final String key = e.getKey();
            String value = e.getValue();
            for (final Map.Entry<String, String> entry : paramEnvMap.entrySet()) {
                value = value.replace("${" + entry.getKey() + "}", entry.getValue());
            }
            return new Pair<>(key, value);

        if (headers != null) {
            final Map<String, List<String>> map = new HashMap<>();
            headers.entrySet().stream().filter(e -> e.getKey() != null).forEach(
                    e -> map.put(e.getKey().toLowerCase(Locale.ROOT), e.getValue() == null ? List.of() : List.copyOf(e.getValue())));
            this.headers = Map.copyOf(map);
        }
    }

    /**

      protected Entry<Class<? extends @NonNull B>, B> delegate() {
        return entry;
      }

      @Override
      @ParametricNullness
      public B setValue(@ParametricNullness B value) {
        cast(getKey(), value);
        return super.setValue(value);
      }
    };
  }

  @Override
  public Set<Entry<Class<? extends @NonNull B>, B>> entrySet() {

            final String hotThreads = response.getNodesMap().entrySet().stream().map(e -> {
                final StringBuilder tempBuf = new StringBuilder();
                append(tempBuf, StringEscapeUtils.escapeJson(e.getKey()), () -> StringEscapeUtils.escapeJson(e.getValue().getHotThreads()));
                return tempBuf.toString();
            }).collect(Collectors.joining(","));
            buf.append(hotThreads).append(',');

        // Act – serialise and parse back
        byte[] bytes = original.toByteArray();
        NegTokenTarg roundTrip = new NegTokenTarg(bytes);

        // Assert – all getters match the original values
        assertEquals(NegTokenTarg.ACCEPT_COMPLETED, roundTrip.getResult(), "result should roundtrip");
        assertEquals(mech, roundTrip.getMechanism(), "mechanism should roundtrip");

It's acceptable for implementation classes to be written to fit into existing code, but new classes must not instantiate managed properties or implement getters manually.

This is preferred:

```groovy
public interface NewThing {
    Property<String> getSomeProperty()
}
```

This is acceptable:

```groovy
public interface NewThing {

public class MultimapKeySetTester<K, V> extends AbstractMultimapTester<K, V, Multimap<K, V>> {
  public void testKeySet() {
    for (Entry<K, V> entry : getSampleElements()) {
      assertTrue(multimap().keySet().contains(entry.getKey()));
    }
  }

  @CollectionSize.Require(absent = ZERO)
  @MapFeature.Require(ALLOWS_NULL_KEYS)
  public void testKeySetContainsNullKeyPresent() {
    initMultimapWithNullKey();

        // Verify that the object was created
        assertNotNull(pacString, "The PacUnicodeString object should not be null.");

        // Verify that the getters return the correct values
        assertEquals(length, pacString.getLength(), "The length should match the value provided in the constructor.");

  }

  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();
  }