### Question:
IdIndexChangeListener implements ChangeListener { @Override public void onAddToCollection(Collection collection, Optional<Vertex> oldVertex, Vertex newVertex) { } IdIndexChangeListener(IndexHandler indexHandler); @Override void onCreate(Collection collection, Vertex vertex); @Override void onPropertyUpdate(Collection collection, Optional<Vertex> oldVertex, Vertex newVertex); @Override void onRemoveFromCollection(Collection collection, Optional<Vertex> oldVertex, Vertex newVertex); @Override void onAddToCollection(Collection collection, Optional<Vertex> oldVertex, Vertex newVertex); @Override void onCreateEdge(Collection collection, Edge edge); @Override void onEdgeUpdate(Collection collection, Edge oldEdge, Edge newEdge);  }### Answer:
@Test public void onAddToCollectionDoesNothing() { Vertex nullVertex = null; instance.onAddToCollection(NULL_COLLECTION, Optional.empty(), nullVertex); verifyZeroInteractions(indexHandler); }