@Test
    @LoadGraphWith(MODERN)
    public void shouldSupportPreExistingComputeKeys() throws Exception {
        final ComputerResult result = graphProvider.getGraphComputer(graph).program(new VertexProgramN()).submit().get();
        result.graph().vertices().forEachRemaining(vertex -> {
            if (vertex.label().equals("person")) {
                if (vertex.value("name").equals("marko"))
                    assertEquals(32, vertex.<Integer>value("age").intValue());
                else if (vertex.value("name").equals("peter"))
                    assertEquals(38, vertex.<Integer>value("age").intValue());
                else if (vertex.value("name").equals("vadas"))
                    assertEquals(30, vertex.<Integer>value("age").intValue());
                else if (vertex.value("name").equals("josh"))
                    assertEquals(35, vertex.<Integer>value("age").intValue());
                else
                    throw new IllegalStateException("This vertex should not have been accessed: " + vertex);
            }
        });
    }
Javadoc for {@code ConcurrentSkipListSet} includes this little note: "Beware that, unlike in most
collections, the size method is not a constant-time operation." Doing a traversal of elements will yield
the correct count. Java 11 upgrade seemed to force this failure consistently.
gremlin-test/src/main/java/org/apache/tinkerpop/gremlin/process/computer/GraphComputerTest.java