anchor.diff:  
   String immediateLoader(int key) => '$key';
   Future<String> futureLoader(int key) => new Future.value(immediateLoader(key));
  -Future<String> delayedLoader(int key) =>
  -    new Future.delayed(const Duration(milliseconds: 10), () => immediateLoader(key));
  +Future<String> delayedLoader(int key) => new Future.delayed(delay, () => immediateLoader(key));
  +String throwingLoader(int key) => throw new UnsupportedError('$key');
   
   // Basic tests that should pass on any (stateless) cache.
   void statelessCacheTests(Cache<int, String> newCache(Loader<int, String> loader)) {
  
positive.code:     return newCache(futureLoader)
          .get(1)
          .then((value) => expect(value, '1', reason: 'get value should be loaded'));
    });
    test('load delayed value', () {
      return newCache(delayedLoader)
  
negative.code: 
  import 'package:more/cache.dart';
  import 'package:test/test.dart';
  
  const delay = const Duration(milliseconds: 10);
  
  // Various common loaders used with the tests.
  String failingLoader(int key) {
  