anchor.diff:          Cache.fifo(loader: loader, maximumSize: 5);
   
       group('constructors', () {
  -      test('missing loader', () {
  -        expect(() => Cache.fifo(), throwsArgumentError);
  -      });
         test('non positive max size', () {
           expect(() => Cache.fifo(loader: immediateLoader, maximumSize: 0),
               throwsArgumentError);
  
positive.code:         Cache.lru(loader: loader, maximumSize: 5);
  
      group('constructors', () {
        test('missing lru', () {
          expect(() => Cache.lru(), throwsArgumentError);
        });
        test('non positive max size', () {
          expect(() => Cache.lru(loader: immediateLoader, maximumSize: 0),
              throwsArgumentError);
  
negative.code:     persistentCacheTests(newUpdateExpireCache);
  
      group('constructors', () {
        test('missing expiry', () {
          expect(
              () => Cache.expiry(loader: immediateLoader), throwsArgumentError);
  