assertEquals(expected.containsKey("b"), map.containsKey("b"));
    assertEquals(expected.get("c"), map.get("c"));
    assertEquals(expected.containsKey("c"), map.containsKey("c"));
  }

  public void testTransformReflectsUnderlyingMap() {
    Map<String, Integer> underlying = new HashMap<>();
    underlying.put("a", 1);
    underlying.put("b", 2);
    underlying.put("c", 3);