assertEqualCharNodes(Iterables.limit(result, 2), "db");
    assertThat(graph.requestedNodes).containsExactly('a', 'a', 'a', 'b', 'b', 'c', 'd', 'd');
  }

  @Test
  @SuppressWarnings("CheckReturnValue")
  public void forTree_acceptsDirectedGraph() throws Exception {
    MutableGraph<String> graph = GraphBuilder.directed().build();
    graph.putEdge("a", "b");

    Traverser.forTree(graph); // Does not throw

    assertEqualCharNodes(Iterables.limit(result, 2), "db");
    assertThat(graph.requestedNodes).containsExactly('a', 'a', 'a', 'b', 'b', 'c', 'd', 'd');
  }

  @Test
  @SuppressWarnings("CheckReturnValue")
  public void forTree_acceptsDirectedGraph() throws Exception {
    MutableGraph<String> graph = GraphBuilder.directed().build();
    graph.putEdge("a", "b");

    Traverser.forTree(graph); // Does not throw

import org.jspecify.annotations.Nullable;

/**
 * Unit test for {@link NullPointerTester}.
 *
 * @author Kevin Bourrillion
 * @author Mick Killianey
 */
@SuppressWarnings({
  "CheckReturnValue",
  "unused", // many methods tested reflectively -- maybe prefer local @Keep annotations?
})
@NullUnmarked
public class NullPointerTesterTest extends TestCase {

  /** Non-NPE RuntimeException. */

      return Optional.of((long) length);
    }

    @Override
    public byte[] read() {
      return Arrays.copyOfRange(bytes, offset, offset + length);
    }

    @SuppressWarnings("CheckReturnValue") // it doesn't matter what processBytes returns here
    @Override
    @ParametricNullness
    public <T extends @Nullable Object> T read(ByteProcessor<T> processor) throws IOException {