Test driven development with a small team

I have a team of 2, me and another dude. For a long time Unit Tests were tricky business and didn't really work with Unity but looking today I saw they're fully working in Unity now. I'm behind on the times I guess.

We've been lazy and have mostly been using lots of play testing and development scenes to isolate features to do our testing, not wanting to waste time learning janky test workflows. So my question is this: For a 2 man team working in our spare time to build a game, how realistic is it to implement a test driven workflow? I'm stuck between that, or just writing tests as needed.

I'm almost entirely self taught on programming with minimal professional environment experience, so I find it challenging in times like this to predict how efficient things will be, which makes planning very difficult.

Thanks in advance for any help.