### Question:
LightUGraph implements UGraph<L>, FastWalkable<L, UNode<L>> { @Override public long numLinks() { return numLinks; } LightUGraph();  LightUGraph(int capacity); @Override int size(); @Override long numLinks(); @Override UNode<L> node(L label); @Override Collection<? extends UNode<L>> nodes(L label); @Override List<? extends UNode<L>> nodes(); @Override Iterable<? extends ULink<L>> links(); @Override UNode<L> add(L label); @Override Set<L> labels(); @Override boolean connected(L from, L to); @Override long state(); String toString(); void compact(int margin); void sort(); static LightUGraph<L> copy(Graph<L> graph); @Override int hashCode(); boolean equals(Object other); @Override UNode<L> get(int i); @SuppressWarnings("unchecked") @Override Class<? extends UGraph<L>> level(); @Override List<UNode<L>> neighborsFast(Node<L> node); static final int NEIGHBOR_CAPACITY; }### Answer:
@Test public void testNumLinks() { UGraph<String> graph = Examples.yeast(); graph = LightUGraph.copy(graph); int numLinks = 0; for(Link<String> link : graph.links()) numLinks++; assertEquals(2277, graph.numLinks()); assertEquals(graph.numLinks(), numLinks); }