Some criminal defense attorneys take the position that the defendant should never testify. This is foolish and I have had great success with the defendant testifying. Of course, if you do it enough, it is bound to blow up in your face. Like anything else in defense work, I only do what it necessary. If it isn’t necessary, don’t take the chance. If you call your client because it was necessary and it blows up in your face, then you are likely in the same position if you didn’t call the defendant anyway.
The best trial run for a defendant is a Miranda hearing (assuming the client made a statement). The defendant can really be put through his paces and see how they handle the witness stand and more importantly, cross examination. In one child pornography case I had, I called my client during the Miranda hearing. The prosecutor destroyed him and from that point on, we decided that he would not be called during trial. Luckily, we won the trial without having to call him because we adapted our strategy well ahead of time.
While I am open to all options, I think the prime scenario for calling a defendant to testify is where he/she made a statement that needs further explanation due to ambiguities that the State can go far with. If these problems are not cleared up, the case may be hopeless. Thankfully, I haven’t had to do this in my own practice but I have seen a few cases on appeal where this was an issue. Again, it should be the last resort. Of course, the final decision as to whether or not the defendant should testify is the defendant’s alone but I have found that almost all will follow their attorney’s advice.