@Test
  public void shouldThrowExceptionOneInDifferentPartition() {
    final Vertex vA = g.addVertex("any", "a");
    final Edge e = vA.addEdge("knows", vA);
    assertEquals(e.id(), g.e(e.id()).id());

    final PartitionGraphStrategy strategy =
        (PartitionGraphStrategy) ((StrategyWrappedGraph) g).strategy().getGraphStrategy().get();
    strategy.clearReadPartitions();

    try {
      g.e(e.id());
    } catch (Exception ex) {
      final Exception expected = Graph.Exceptions.elementNotFound(Edge.class, e.id());
      assertEquals(expected.getClass(), ex.getClass());
      assertEquals(expected.getMessage(), ex.getMessage());
    }
  }
  @Test
  public void shouldWriteToMultiplePartitions() {
    final Vertex vA = g.addVertex("any", "a");
    final Vertex vAA = g.addVertex("any", "aa");
    final Edge eAtoAA = vA.addEdge("a->a", vAA);

    final PartitionGraphStrategy strategy =
        (PartitionGraphStrategy) ((StrategyWrappedGraph) g).strategy().getGraphStrategy().get();
    strategy.setWritePartition("B");
    final Vertex vB = g.addVertex("any", "b");
    vA.addEdge("a->b", vB);

    strategy.setWritePartition("C");
    final Vertex vC = g.addVertex("any", "c");
    final Edge eBtovC = vB.addEdge("b->c", vC);
    final Edge eAtovC = vA.addEdge("a->c", vC);

    /* not applicable to SubgraphStrategy
    final GraphTraversal t = g.V();
    assertTrue(t.strategies().get().stream().anyMatch(o -> o.getClass().equals(PartitionGraphStrategy.PartitionGraphTraversalStrategy.class)));
    */

    strategy.clearReadPartitions();
    assertEquals(new Long(0), g.V().count().next());
    assertEquals(new Long(0), g.E().count().next());

    strategy.addReadPartition("A");
    assertEquals(new Long(2), g.V().count().next());
    assertEquals(new Long(1), g.E().count().next());
    assertEquals(new Long(1), g.v(vA.id()).outE().count().next());
    assertEquals(eAtoAA.id(), g.v(vA.id()).outE().next().id());
    assertEquals(new Long(1), g.v(vA.id()).out().count().next());
    assertEquals(vAA.id(), g.v(vA.id()).out().next().id());

    strategy.addReadPartition("B");
    assertEquals(new Long(3), g.V().count().next());
    assertEquals(new Long(2), g.E().count().next());

    strategy.addReadPartition("C");
    assertEquals(new Long(4), g.V().count().next());
    assertEquals(new Long(4), g.E().count().next());

    strategy.removeReadPartition("A");
    strategy.removeReadPartition("B");

    assertEquals(new Long(1), g.V().count().next());
    // two edges are in the "C" partition, but one each of their incident vertices are not
    assertEquals(new Long(0), g.E().count().next());

    assertEquals(new Long(0), g.v(vC.id()).inE().count().next());
    assertEquals(new Long(0), g.v(vC.id()).in().count().next());

    strategy.addReadPartition("B");
    // only one edge in, due to excluded vertices; vA is not in {B,C}
    assertEquals(new Long(1), g.v(vC.id()).inE().count().next());
    assertEquals(new Long(1), g.v(vC.id()).in().count().next());
    assertEquals(vC.id(), g.e(eBtovC.id()).inV().id().next());
    assertEquals(vB.id(), g.e(eBtovC.id()).outV().id().next());
    assertEquals(vC.id(), g.e(eAtovC.id()).inV().id().next());
    assertFalse(g.e(eAtovC.id()).outV().hasNext());

    /* not applicable to SubgraphStrategy
    strategy.addReadPartition("A");
    g.v(vA.id()).out().out().forEach(v -> {
        assertTrue(v instanceof StrategyWrapped);
        assertFalse(((StrategyWrappedElement) v).getBaseElement() instanceof StrategyWrapped);
    });

    g.v(vA.id()).outE().inV().outE().forEach(e -> {
        assertTrue(e instanceof StrategyWrapped);
        assertFalse(((StrategyWrappedElement) e).getBaseElement() instanceof StrategyWrapped);
    });
    */
  }