/// <inheritdoc />
        protected override string GetMessage(Commands.Add.Add command)
        {
            if (command == null)
            {
                return($"expected added entity {_explanation}, but story unexpectedly ends");
            }
            if (command.EntityType != typeof(T))
            {
                return
                    ($"expected added entity of type {typeof(T).Name} and {_explanation}, but got one of {command.EntityType.Name}");
            }

            if (string.IsNullOrEmpty(_explanation))
            {
                return($"added {typeof(T).Name} does not satisfy conditions");
            }
            return($"addition '{_explanation}' does not satisfy condition");
        }