What is the test for a finding of ineffective counsel?

"Reviewing courts defer to counsel's reasonable tactical decisions in examining a claim of ineffective assistance of counsel [citation], and there is a 'strong presumption that counsel's conduct falls within the wide range of reasonable professional assistance.' [Citation.]" (People v. Lucas (1995) 12 Cal.4th 415, 436-437.) "'Reviewing courts will reverse convictions on the ground of inadequate counsel only if the record on appeal affirmatively discloses that counsel had no rational tactical purpose for his act or omission.' [Citation.]" (People v. Zapien (1993) 4 Cal.4th 929, 980.)