When will Trump testify in his Impeachment hearings?

When the coast is clear, which might not be until Mar de Lago freezes over.

If he's the genius he claims to be, never. He'll perjure himself.

Never. If he testifies and he has to tell the truth but he knowingly lies then that can send him to jail for lying under oath. 

If he has a good lawyer, he would never be allowed to testify. If he’s asked a question and he plead the 5th, how does that make him look. If he testifies, he’s open to all sort of questions. 

Never. He will pretext having to attend phase 2 of his "physical"...

The fat one is a coward.

Trump was invited to testify, under oath, by the Mueller investigation.  He wanted to do it, so his lawyers held some practice Q-and-A sessions with him pretending he was under oath.

What they found was that he wasn't able to stick to the truth even when he was trying!  The lawyers told him if he testified under oath he'd end up in prison for sure.

Trump has been a liar all his life.  It's just part of his style, how he operates.  I think sometimes he doesn't even realize he's lying.  So I think it's very unlikely he will testify under oath.  If he does, you'll know he's truly desperate.

Right after he locks Hillary up, builds his wall and release his taxes when the audit is finished. That puts the timeframe sometime in the next century 

Probably never.  He's too much of a coward and knows he's guilty.