### Question:
HMapIS implements MapIS, Cloneable, Serializable { @Override public void plus(MapIS m) { for (MapIS.Entry e : m.entrySet()) { int key = e.getKey(); if (this.containsKey(key)) { this.put(key, (short) (this.get(key) + e.getValue())); } else { this.put(key, e.getValue()); } } } HMapIS(int initialCapacity, float loadFactor);  HMapIS(int initialCapacity);  HMapIS();  HMapIS(MapIS m); @Override int size(); @Override boolean isEmpty(); @Override short get(int key); @Override boolean containsKey(int key); @Override short put(int key, short value); @Override void putAll(MapIS m); @Override short remove(int key); @Override void clear(); @Override boolean containsValue(short value); @Override Object clone(); @Override Set<Integer> keySet(); @Override Collection<Short> values(); @Override Set<MapIS.Entry> entrySet(); @Override String toString(); @Override void plus(MapIS m); @Override long dot(MapIS m); @Override void increment(int key); @Override void increment(int key, short value); MapIS.Entry[] getEntriesSortedByValue(); MapIS.Entry[] getEntriesSortedByValue(int n);  }### Answer:
@Test public void testPlus() throws IOException { HMapIS m1 = new HMapIS(); m1.put(1, (short) 5); m1.put(2, (short) 22); HMapIS m2 = new HMapIS(); m2.put(1, (short) 4); m2.put(3, (short) 5); m1.plus(m2); assertEquals(m1.size(), 3); assertTrue(m1.get(1) == 9); assertTrue(m1.get(2) == 22); assertTrue(m1.get(3) == 5); }