What is the test for establishing constitutionally inadequate assistance?

The defendant bears the burden of establishing constitutionally inadequate assistance. (People v. Carter (2005) 36 Cal.4th 1114, 1189) "'A reviewing court will indulge in a presumption that counsel's performance fell within the wide range of professional competence and that counsel's actions and inactions can be explained as a matter of sound trial strategy. . . . If the record on appeal sheds no light on why counsel acted or failed to act in the manner challenged, an appellate claim of ineffective assistance of counsel must be rejected unless counsel was asked for an explanation and failed to provide one, or there simply could be no satisfactory explanation.'" (Ibid.)