### Question:
LightWeightLinkedSet extends LightWeightHashSet<T> { public T pollFirst() { if (head == null) { return null; } T first = head.element; this.remove(first); return first; } LightWeightLinkedSet(int initCapacity, float maxLoadFactor,
      float minLoadFactor);  LightWeightLinkedSet(); T pollFirst(); @Override List<T> pollN(int n); @Override List<T> pollAll(); @Override @SuppressWarnings("unchecked") U[] toArray(U[] a); @Override Iterator<T> iterator(); @Override void clear();  }### Answer:
@Test public void testPollOneElement() { LOG.info("Test poll one element"); set.add(list.get(0)); assertEquals(list.get(0), set.pollFirst()); assertNull(set.pollFirst()); LOG.info("Test poll one element - DONE"); }