@Test
  public void addANodeAndSampleableGoesUp() {
    addPropertyToReferenceNode();

    assertThat(sampleable.getValue(), is(1d));

    addNodeIntoGraph();
    addNodeIntoGraph();

    assertThat(sampleable.getValue(), is(3d));
  }
 @Test
 public void emptyDbHasZeroNodesInUse() {
   assertThat(sampleable.getValue(), is(0d));
 }