What is the test for admitting an uncharged crime?

"To be admissible on the issue of identity, an uncharged crime must be highly similar to the charged offenses, so similar as to serve as a signature or fingerprint. [Citations.]" (People v. Barnwell, supra, 41 Cal.4th at p. 1056; see also People v. Harris (2013) 57 Cal.4th 804, 841 [" 'The greatest degree of similarity is required for evidence of uncharged misconduct to be relevant to prove identity. For identity to be established, the uncharged misconduct and the charged offense must share common features that are sufficiently distinctive so as to support the inference that the same person committed both acts. [Citation.] "The pattern and characteristics of the crimes must be so unusual and distinctive as to be like a signature." [Citation.]' "].) We cannot conclude, on the record before us, that defendant's previous illegal possession of a .357 caliber revolver was so unusual or distinctive as to serve as a signature or fingerprint admissible to prove his identity as to the robber who used a .32 caliber revolver. We therefore conclude that defendant's statements about having been "caught with" revolvers in the past should not have been admitted. Even so, we conclude that the error was harmless.