What is the test for instructing a jury on the general principles of law in a criminal case?

" 'It is settled that in criminal cases, even in the absence of a request, the trial court must instruct on the general principles of law relevant to the issues raised by the evidence. [Citations.] The general principles of law governing the case are those principles closely and openly connected with the facts before the court, and which are necessary for the jury's understanding of the case.' [Citation.]" (People v. Wickersham (1982) 32 Cal.3d 307, 323, 185 Cal.Rptr. 436, 650 P.2d 311.)