A workaround I've used sometimes to retrigger CI is to do `git commit --amend --no-edit --reset-author`. This changes the sha by changing the author timestamp. Then you can force push it to the PR branch
I think the person you're replying to is saying that "fully implement every unit test up front" does not describe TDD. With TDD you continuously alternate between writing tests and writing production code. It's not like you write a whole test suite up front.