“"the Testimony Of The Defendant Has To Be Believed" ???”

As per Eric Lai in thestar.com:

"The Supreme Court had held that the testimony of the defendant, unshaken under cross-examination, is to be believed."

Is that true?

Somewhat oversimplified by Lai, but yes. Case law basically states that the Crown witnesses shouldn't be given any more weight than defence witnesses if both are equally credible. For typical HTA purposes, it basically means the evidence of the police shouldn't be considered any more credible by virtue of their occupation.

The key is credibility. Simply taking the stand and saying "I didn't do it" probably won't cut it. You'll need to provide a clear explanation of what took place. If your version of events is considered to be as credible as the officers, then it creates reasonable doubt. The Court can still believe the officer, but no more so then the defendant.

As with all things HTA, your success with this tactic will vary depending on the jurisdiction and J.P.