How to handle training on a specific technology in Scrum?

My team is making the transition to Scrum.

I am facing an issue I still not found on the various Scrum resources I've been studying: how to manage training?

I express myself by example:

my team has 4 developers, 2 of them know nothing about Test Driven Development
the project must be done using TDD

Should I create a backlog item "Study TDD" and use the first sprints so that the untrained developers learn TDD?

Or should I remove the developers from the project until they completed the training? Which is the best practice in this case?

Solution

Just send them to the training, and continue your sprints as normal. While they are in training they won't contribute to the velocity, the same as if they were sick or on vacation or just having a bad day. The velocity isn't a goal so much it's an indicator.

You can create a story for training if you want, but it isn't necessary. If creating the story helps, by all means do it. Don't do it just because you think you're supposed to. I've been on teams that liked to track non-product tasks, and teams that didn't. Do what your team decides to do.

In your question you wrote:

the project must be done using TDD

I hope that's because the team decided that, and it wasn't something that was decided for them. The whole point of scrum is to build a team that can make these decisions for themselves.