DocMap docMap = new DocMap(parentMap);

        assertTrue(docMap.isEmpty());
        assertEquals(0, docMap.size());

        docMap.put("key1", "value1");
        assertFalse(docMap.isEmpty());
        assertEquals(1, docMap.size());

        docMap.put("key2", "value2");
        assertFalse(docMap.isEmpty());
        assertEquals(2, docMap.size());

        docMap.clear();

    public boolean isEmpty() {
        return entry == null || vertices == null || vertices.isEmpty();
    }

    // ------------------------------------------------------------------------
    public boolean isEmptyEdges() {
        return isEmpty() || incidentEdges == null || incidentEdges.isEmpty();
    }

    assertThat(network.adjacentNodes(N2)).isEmpty();
    assertThat(network.predecessors(N2)).isEmpty();
    assertThat(network.successors(N2)).isEmpty();
    assertThat(network.incidentEdges(N2)).isEmpty();
    assertThat(network.inEdges(N2)).isEmpty();
    assertThat(network.outEdges(N2)).isEmpty();
    assertThat(network.adjacentNodes(N4)).isEmpty();
    assertThat(network.predecessors(N4)).isEmpty();

    redQueue.execute("task", 100.µs) {
      log += "run@${taskFaker.nanoTime}"
    }

    taskFaker.advanceUntil(0.µs)
    assertThat(log).isEmpty()

    redQueue.cancelAll()

    taskFaker.advanceUntil(99.µs)
    assertThat(log).isEmpty()

    taskFaker.assertNoMoreTasks()

    assertThat(testLogHandler.takeAll()).containsExactly(
      "FINE: Q10000 scheduled after 100 µs: task",

     */
    public static final boolean isEmpty(final String text) {
        return text == null || text.length() == 0;
    }

    /**
     * Checks if the string is not empty.
     *
     * @param text the string to check
     * @return true if not empty, false otherwise
     */
    public static final boolean isNotEmpty(final String text) {
        return !isEmpty(text);
    }

    /**

    assertTrue(ArbitraryInstances.get(NavigableMap.class).isEmpty());
    assertTrue(ArbitraryInstances.get(LinkedList.class).isEmpty());
    assertTrue(ArbitraryInstances.get(Deque.class).isEmpty());
    assertTrue(ArbitraryInstances.get(Queue.class).isEmpty());
    assertTrue(ArbitraryInstances.get(PriorityQueue.class).isEmpty());
    assertTrue(ArbitraryInstances.get(BitSet.class).isEmpty());

            return Iterators.size(iterator());
          }

          @Override
          public boolean isEmpty() {
            return !iterator().hasNext();
          }
        };
      }

      Iterator<Entry<Range<K>, V>> entryIterator() {
        if (subRange.isEmpty()) {
          return emptyIterator();
        }
        Cut<K> cutToStart =
            MoreObjects.firstNonNull(

    assertEquals(OPEN, range.lowerBoundType());
    assertTrue(range.hasUpperBound());
    assertEquals(8, (int) range.upperEndpoint());
    assertEquals(OPEN, range.upperBoundType());
    assertFalse(range.isEmpty());
    assertEquals("(4..8)", range.toString());
    reserializeAndAssert(range);
  }

  public void testOpen_invalid() {
    assertThrows(IllegalArgumentException.class, () -> Range.open(4, 3));

    assertTrue(ArbitraryInstances.get(NavigableMap.class).isEmpty());
    assertTrue(ArbitraryInstances.get(LinkedList.class).isEmpty());
    assertTrue(ArbitraryInstances.get(Deque.class).isEmpty());
    assertTrue(ArbitraryInstances.get(Queue.class).isEmpty());
    assertTrue(ArbitraryInstances.get(PriorityQueue.class).isEmpty());
    assertTrue(ArbitraryInstances.get(BitSet.class).isEmpty());

    // source node and the second is the target node
    assertThat(network.edgesConnecting(N2, N1)).isEmpty();
  }

  @Test
  public void inEdges_oneEdge() {
    addEdge(N1, N2, E12);
    assertThat(network.inEdges(N2)).containsExactly(E12);
    // Edge direction handled correctly
    assertThat(network.inEdges(N1)).isEmpty();
  }

  @Test
  public void outEdges_oneEdge() {
    addEdge(N1, N2, E12);