Franks comments on my prior comments is getting afield of the topic... however to clarify from an experienced criminal prosecutor and defense attorney, smartly worded statements to the law enforcement before invoking can be elicited through the police and detectives through effective direct or cross examination, thereby eliminating any need to have the accused testify.
Q: And isn't it true Detective Johnson, that Mr. Smith told you that the deceased came at him with a knife in the parking lot?
A: Yes
Q: And Mr. Smith told you that he told the aggressor to stop at least three times?
A: Yes, that's what he said.
Q: But the man with a knife kept coming and didn't stop?
A: That was Mr. Smith's version.
Q: And he said he feared for his life so he drew his pistol?
A: Yes
Q: And he has a lawful concealed carry permit?
A: Yes
Q: And the requisite training?
A: Yes
Q: And the ammunition used was XYZ?
A: Yes
Q: And that's identical or very similar to what the police carry in their guns?
A: Yes
Q: And in your investigation, you determined that both shots were fired at about 10' distance, in rapid succession, while the deceased was standing?
A: Yes
Q: And when you talked to witness ABC, she told you that a version of events that is generally consistent with what Mr. Smith had told you?
A: Yes
Q: When you talked to Mr. Smith at the scene, he told you he acted in self defense?
A: Yes
Q: And he told you that he wanted to press charges against the attacker for assault?
A: Yes
You get the idea. The same would be done with the forensics scientists, other experts, witnesses, etc.
There would be little, if anything, an accused to add to this by his testimony, and many times accused people look shady when testifying, or just say REALLY DUMB things on the stand, and this can sink them. Call it nerves, or trying to impress, or being tricked into getting angry, etc.
An accused should rarely need to testify if the event was justified (forensics will most likely tell a clear story) and a person is intelligent about what he says to the police before invoking.
Sorry to take this afield, but it's an important understanding of criminal law.