What is the test for a claim of inadequate assistance of counsel?

We reject defendant's claim of inadequate assistance of counsel for lack of an adequate showing of prejudice. "In any case, when considering a claim of ineffective assistance of counsel, 'a court need not determine whether counsel's performance was deficient before examining the prejudice suffered by the defendant as a result of the alleged deficiencies.... If it is easier to dispose of an ineffectiveness claim on the ground of lack of sufficient prejudice, which we expect will often be so, that course should be followed.' [Citation.] A defendant must prove prejudice that is a ' "demonstrable reality," not simply speculation.' [Citations.]" (People v. Fairbank (1997) 16 Cal.4th 1223, 1241.)