What is the test for tortfeasors to determine whether an employee is entitled to claim damages from his employer if he injures himself while working in the same business at the same time?

[Citation.] Moreover, '"where the employee is combining his own business with that of his employer, or attending to both at substantially the same time, no nice inquiry will be made as to which business he was actually engaged in at the time of injury, unless it clearly appears that neither directly nor indirectly could he have been serving his employer." [Citations.]' [Citation.] . . . [A]n employee's tortious act may be within the scope of employment even if it contravenes an express company rule and confers no benefit to the employer. [Citation.]" (Farmers Ins. Group v. County of Santa Clara (1995) 11 Cal.4th 992, 1004.)