### Question:
BidirectionalHashMap { public Map<V, K> reversed() { return Collections.unmodifiableMap(valueToKey); } BidirectionalHashMap(Map<K, V> keyToValue); Map<K, V> forward(); Map<V, K> reversed();  }### Answer:
@Test public void testReverse() throws Exception { HashMap<String, Integer> stringIntegerMap = new HashMap<>(3); stringIntegerMap.put("Hello", 1); stringIntegerMap.put("Hi", 3); stringIntegerMap.put("Hey!", 6); BidirectionalHashMap<Integer, String> testee = new BidirectionalHashMap<>(integerStringMap); assertEquals(stringIntegerMap, testee.reversed()); }