This was the question asked by Dr. David Wilson in his recent posting. Rather than focus on behavior change per se, I suggest a better outcome measure to answer Dr. Wilson's question is reduced HIV transmission. Thus the hypothesis would be that testing reduces HIV transmission via a change in sexual behavior or blood practices. Once treatment comes into the picture, the potential benefits of testing to induce preventive behavior becomes clouded. Hence the peer reviewed publication that Dr. Wilson is asking for should either be studies done in wealthier countries before 1995-96 when more effective therapy started to appear, or coming from the developing world where treatment is not available.
Most researchers agree that the best proof of a hypothesis comes from randomized clinical trials.
In such a trial, the different participating groups should have the same inherent risk of HIV independent of whether or not they received testing. While the information would be useful, doing such a trial would be difficult due to ethical considerations. For example, assume that HIV infected person were identified in a blood testing program in developing country XXX where expensive treatments are not available. The researchers would then follow both groups over time. Because the outcome of interest is further HIV transmission to others, the study would be difficult to do unless the sexual partners were also included, which adds to the complexity and expense of the study.