public void GetItem_NullRElativePath_ThrowArgumentNullException(string defaultValue)
 {
   var repository = new DictionaryPhraseRepository(new Dictionary());
   repository.Invoking(x => x.GetItem(null, defaultValue)).ShouldThrow<ArgumentNullException>();
 }
    public void Get_IncorrectRelativePath_ThrowArgumentException(Db db, [Content]Item rootItem, string defaultValue)
    {
      //Arrange
      var relativePath = "/";
      var repository = new DictionaryPhraseRepository(new Dictionary() { Root = rootItem, AutoCreate = true });

      //Assert
      repository.Invoking(x=>x.Get(relativePath, defaultValue)).ShouldThrow<ArgumentException>();
    }