What is the test for 'unavailable as a witness' under the Colorado Evidence Code?

Evidence Code, section 240, so far as pertinent herein, provides that a declarant who is '(e)xempted or precluded on the ground of privilege from testifying concerning the matter to which his statement is relevant' is 'unavailable as a witness.' In other words, a witness whose Testimony is not available, even though he is present at the trial, is 'unavailable as a witness' within the meaning of Evidence Code, section 1291. (Cf. Johnson v. People (1963) 152 Colo. 586, 384 P.2d 454.)