What is the test for establishing a separate corporate entity?

'In order to cast aside the legal fiction of distinct corporate existence as distinguished from those who own its capital stock, it is not enough that it is so organized and controlled and its affairs so managed as to make it 'merely an instrumentality, conduit, or adjunct' of its stockholders, but it must further appear that they are the 'business conduits and alter ego of one another,' and that to recognize their separate entities would aid the consummation of a wrong. * * *" (See also Riddle v. Leuschner, 51 Cal.2d 574, 582, 335 P.2d 107.)