* <p>Values do not have to be unique. However, values must be non-null.
     *
     * <p>If either or both endpoints are not already present in this graph, this method will
     * silently {@link #addNode(Object) add} each missing endpoint to the graph.
     *
     * @return this {@code Builder} object
     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
     *     #allowsSelfLoops()}

    putEdge(N1, N2);

    assertThat(graphAsMutableGraph.putEdge(N2, N1)).isFalse();
  }

  /**
   * Tests that the method {@code putEdge} will silently add the missing nodes to the graph, then
   * add the edge connecting them. We are not using the proxy methods here as we want to test {@code
   * putEdge} when the end-points are not elements of the graph.
   */
  @Test

    }
  }

  public static class ImmutableSetWithBadHashesGenerator extends TestCollidingSetGenerator
      // Work around a GWT compiler bug.  Not explicitly listing this will
      // cause the createArray() method missing in the generated javascript.
      // TODO: Remove this once the GWT bug is fixed.
      implements TestCollectionGenerator<Object> {
    @Override
    public Set<Object> create(Object... elements) {

    assertThat(e).hasMessageThat().contains(ERROR_SELF_LOOP);
  }

  /**
   * This test checks an implementation dependent feature. It tests that the method {@code addEdge}
   * will silently add the missing nodes to the graph, then add the edge connecting them. We are not
   * using the proxy methods here as we want to test {@code addEdge} when the end-points are not
   * elements of the graph.
   */
  @Test

    assertEquals(multimap.hashCode(), unmodifiable.hashCode());
    assertEquals(multimap, unmodifiable);

    assertThat(unmodifiable.asMap().get("bar")).containsExactly(5, -1);
    assertNull(unmodifiable.asMap().get("missing"));

    assertFalse(unmodifiable.entries() instanceof Serializable);
  }

  /** Prepares the multimap for unmodifiable tests, returning an unmodifiable view of the map. */

    assertThat(e).hasMessageThat().contains(ERROR_SELF_LOOP);
  }

  /**
   * This test checks an implementation dependent feature. It tests that the method {@code addEdge}
   * will silently add the missing nodes to the graph, then add the edge connecting them. We are not
   * using the proxy methods here as we want to test {@code addEdge} when the end-points are not
   * elements of the graph.
   */
  @Test

            IllegalArgumentException.class, () -> graph.removeEdge(EndpointPair.ordered(2, 1)));
    assertThat(e).hasMessageThat().contains(ENDPOINTS_MISMATCH);
  }

  @Test
  public void edgeValue_missing() {
    graph = ValueGraphBuilder.directed().build();

    assertThat(graph.edgeValueOrDefault(1, 2, DEFAULT)).isEqualTo(DEFAULT);
    assertThat(graph.edgeValueOrDefault(2, 1, DEFAULT)).isEqualTo(DEFAULT);

    assertThat(e).hasMessageThat().contains(ERROR_SELF_LOOP);
  }

  /**
   * This test checks an implementation dependent feature. It tests that the method {@code addEdge}
   * will silently add the missing nodes to the graph, then add the edge connecting them. We are not
   * using the proxy methods here as we want to test {@code addEdge} when the end-points are not
   * elements of the graph.
   */
  @Test

import java.util.Set;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

/**
 * Tests for {@link Graphs}. Tests assume that the implementation of the method {@code addEdge} adds
 * the missing nodes to the graph, then adds the edge between them.
 */
@RunWith(JUnit4.class)
public class GraphsTest {
  private static final Integer N1 = 1;
  private static final Integer N2 = 2;

    assertEquals(multimap.hashCode(), unmodifiable.hashCode());
    assertEquals(multimap, unmodifiable);

    assertThat(unmodifiable.asMap().get("bar")).containsExactly(5, -1);
    assertNull(unmodifiable.asMap().get("missing"));

    assertFalse(unmodifiable.entries() instanceof Serializable);
  }

  /** Prepares the multimap for unmodifiable tests, returning an unmodifiable view of the map. */