public void testMerge_recurse() {
  cache = CacheBuilder.newBuilder().build();
  cache.put(key, "1");

  // As we cannot provide immediate checking without an expensive solution, e.g. ThreadLocal,
  // instead we assert that a stack overflow error will occur to inform the developer (vs
  // a live-lock or deadlock alternative).
  BiFunction<String, String, String> mappingFunction =
      new BiFunction<String, String, String>() {
        int recursed;

        @Override public String apply(String oldValue, String value) {
          if (++recursed == 2) {
            throw new StackOverflowError();
          }
          return cache.asMap().merge(key, "1", this);
        }
      };
  try {
    cache.asMap().merge(key, "1", mappingFunction);
    Assert.fail();
  } catch (StackOverflowError e) {}
}