### Question:
Int2IntOpenHashMapWritable extends Int2IntOpenHashMap implements Writable { public void increment(int key) { increment(key, 1); } Int2IntOpenHashMapWritable(); @Override void readFields(DataInput in); void decode(); boolean hasBeenDecoded(); @Override void write(DataOutput out); byte[] serialize(); static Int2IntOpenHashMapWritable create(DataInput in); static Int2IntOpenHashMapWritable create(byte[] bytes); void plus(Int2IntOpenHashMapWritable m); long dot(Int2IntOpenHashMapWritable m); void increment(int key); void increment(int key, int n); static void setLazyDecodeFlag(boolean b); static boolean getLazyDecodeFlag(); int[] getKeys(); int[] getValues(); void lazyplus(Int2IntOpenHashMapWritable m); Int2IntMap.Entry[] getEntriesSortedByValue(); Int2IntMap.Entry[] getEntriesSortedByValue(int k);  }### Answer:
@Test public void testIncrement() throws IOException { Int2IntOpenHashMapWritable m = new Int2IntOpenHashMapWritable(); m.put(2, 7); m.put(1, 29); assertEquals(7, m.get(2)); assertEquals(29, m.get(1)); m.increment(2); m.increment(1); m.increment(3); assertEquals(8, m.get(2)); assertEquals(30, m.get(1)); assertEquals(1, m.get(3)); m.increment(1, 3); m.increment(3, 5); assertEquals(8, m.get(2)); assertEquals(33, m.get(1)); assertEquals(6, m.get(3)); }