anchor.diff:  
   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) {
  
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:         .then((_) => cache.get(1))
          .then((value) => expect(value, 'foo', reason: 'updated value'));
    });
    test('load throwing value has no side-effect', () {
      var cache = newCache(throwingLoader);
      return cache
          .get(1)
          .catchError((exception) => '1')
          .then((_) => cache.getIfPresent(1))
          .then((value) => expect(value, isNull, reason: 'loader threw exception'));
    });
    test('set and get', () {
      var cache = newCache(failingLoader);
      return cache
  