### Question:
B2Collections { public static <K,V> Map<K, V> mapOf() { return new TreeMap<>(); }  static Set<T> unmodifiableSet(T[] elements); static Map<K,V> unmodifiableMap(Map<K,V> orig); static Map<K, V> mapOf(); static Map<K, V> mapOf(K k1, V v1); static Map<K, V> mapOf(K k1, V v1,
                                        K k2, V v2); static Map<K, V> mapOf(K k1, V v1,
                                        K k2, V v2,
                                        K k3, V v3); @SafeVarargs static List<T> listOf(T... orig);  }### Answer:
@Test public void testMapOf() { final Map<String, Integer> empty = B2Collections.mapOf(); assertEquals(0, empty.size()); final Map<String, Integer> one = B2Collections.mapOf("a", 1); assertEquals(1, one.size()); assertEquals((Integer) 1, one.get("a")); final Map<String, Integer> two = B2Collections.mapOf( "a", 1, "b", 2); assertEquals(2, two.size()); assertEquals((Integer) 1, two.get("a")); assertEquals((Integer) 2, two.get("b")); final Map<String, Integer> three = B2Collections.mapOf( "a", 1, "b", 2, "c", 3); assertEquals(3, three.size()); assertEquals((Integer) 1, three.get("a")); assertEquals((Integer) 2, three.get("b")); assertEquals((Integer) 3, three.get("c")); }