private void assertVadasAsOnlyValueReturned(final Traversal<Vertex, Vertex> traversal) {
        printTraversalForm(traversal);
        assertThat(traversal.hasNext(), is(true));
        assertEquals(convertToVertexId("vadas"), traversal.next().id());
        assertThat(traversal.hasNext(), is(false));
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-test/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/filter/HasTest.java