public void RemovingAllElementsOfKeyWillAlsoRemoveKey()
 {
     Fixture.Add(0, "hello");
     Fixture.Add(0, "cat");
     Fixture.Add(0, "dog");
     Fixture.Remove(0, "dog");
     Fixture.Remove(0, "cat");
     Fixture.Remove(0, "hello");
     Fixture.Contains(0).Should().Be(false);
 }
 public IEnumerator <Value> GetEnumerator()
 {
     if (!_source.Contains(_key))
     {
         yield break;
     }
     else
     {
         foreach (var item in _source[_key])
         {
             yield return(item);
         }
     }
 }