checkArgument(!result.containsKey(entry.getKey()));
        result.put(entry.getKey(), entry.getValue());
      }
      return result;
    }
  }

  static class TestBiMap<K, V> extends TestMap<K, V> implements BiMap<K, V> {
    private final BiMap<K, V> delegate;

    public TestBiMap(BiMap<K, V> delegate, Object mutex) {
      super(delegate, mutex);
      this.delegate = delegate;
    }

        checkArgument(!result.containsKey(entry.getKey()));
        result.put(entry.getKey(), entry.getValue());
      }
      return result;
    }
  }

  static class TestBiMap<K, V> extends TestMap<K, V> implements BiMap<K, V> {
    private final BiMap<K, V> delegate;

    public TestBiMap(BiMap<K, V> delegate, Object mutex) {
      super(delegate, mutex);
      this.delegate = delegate;
    }