What is the test for disclosing the name of an informant who is a material witness in a criminal case?

"[T]he prosecution must disclose the name of an informant who is a material witness in a criminal case or suffer dismissal of the charges against the defendant. [Citation.] An informant is a material witness if there appears, from the evidence presented, a reasonable possibility that he or she could give evidence on the issue of guilt that might exonerate the defendant. [Citation.] The defendant bears the burden of adducing ' " 'some evidence' " ' on this score." (People v. Lawley (2002) 27 Cal.4th 102, 159.)