// Force close the handle
                this.open = false;
                this.usageCount.set(0);

                // Clear mutable references to free memory
                // Note: Some fields may be final and cannot be nulled

                // Clear any other mutable state would go here
            }
        } catch (Exception e) {
            log.error("Failed to perform emergency file handle cleanup", e);

 * errors for using {@code get(Comparator.class)} as a {@code Comparator<Foo>}, for example.
 * Immutable empty instances are returned for collection types; {@code ""} for string; {@code 0} for
 * number types; reasonable default instance for other stateless types. For mutable types, a fresh
 * instance is created each time {@code get()} is called.
 *
 * @author Kevin Bourrillion
 * @author Ben Yu

   *
   * <p>This method returns a mutable {@code List}. For an {@code ImmutableList}, use {@code
   * Resources.asCharSource(url, charset).readLines()}.
   *
   * @param url the URL to read from
   * @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
   *     helpful predefined constants
   * @return a mutable {@link List} containing all the lines

 */
@NullUnmarked
public abstract class AbstractNetworkTest {

  Network<Integer, String> network;

  /**
   * The same reference as {@link #network}, except as a mutable network. This field is null in case
   * {@link #createGraph()} didn't return a mutable network.
   */
  MutableNetwork<Integer, String> networkAsMutableNetwork;

  static final Integer N1 = 1;
  static final Integer N2 = 2;
  static final Integer N3 = 3;

   * @return an immutable set containing those elements, minus duplicates
   */
  public static <E extends Enum<E>> ImmutableSet<E> immutableEnumSet(
      E anElement, E... otherElements) {
    return ImmutableEnumSet.asImmutable(EnumSet.of(anElement, otherElements));
  }

  /**
   * Returns an immutable set instance containing the given enum elements. Internally, the returned

   *     those lists should appear in the resulting lists
   * @param <B> any common base class shared by all axes (often just {@link Object})
   * @return the Cartesian product, as an immutable list containing immutable lists
   * @throws IllegalArgumentException if the size of the cartesian product would be greater than
   *     {@link Integer#MAX_VALUE}

    @Test
    @DisplayName("ltime field is mutable")
    void testLtimeField() {
        TestLocking t = new TestLocking();

        // Initial value
        assertEquals(0L, t.ltime, "ltime should start at 0");

        // Set new value
        long currentTime = System.currentTimeMillis();
        t.ltime = currentTime;
        assertEquals(currentTime, t.ltime, "ltime should be mutable");
    }

    @Test

        if (subgraph.nodes().contains(successorNode)) {
          subgraph.addEdge(node, successorNode, edge);
        }
      }
    }
    return subgraph;
  }

  /** Creates a mutable copy of {@code graph} with the same nodes and edges. */
  public static <N> MutableGraph<N> copyOf(Graph<N> graph) {
    MutableGraph<N> copy = GraphBuilder.from(graph).expectedNodeCount(graph.nodes().size()).build();

        if (subgraph.nodes().contains(successorNode)) {
          subgraph.addEdge(node, successorNode, edge);
        }
      }
    }
    return subgraph;
  }

  /** Creates a mutable copy of {@code graph} with the same nodes and edges. */
  public static <N> MutableGraph<N> copyOf(Graph<N> graph) {
    MutableGraph<N> copy = GraphBuilder.from(graph).expectedNodeCount(graph.nodes().size()).build();

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import org.jspecify.annotations.NonNull;
import org.jspecify.annotations.Nullable;

/**
 * A mutable type-to-instance map. See also {@link ImmutableTypeToInstanceMap}.
 *
 * @author Ben Yu
 * @since 13.0
 */
public final class MutableTypeToInstanceMap<B extends @Nullable Object>