Well, I mainly work in a team where developers ship separate products for the internal usage. So it's not really working in a team. Products are generally quite technical - it's not your usual CRUD shop.

I do write tests, but only post-factum, when I know for sure this component will be re-used in other components. I write them in cases where I know I will forget about the certain edge-cases in some time, so changing the code will most certainly introduce bugs.

When you have components that are reused over the course of several years (and obviously being optimised if the requirement is there), the chance of regressions is severely increased.

So I see that "writing tests for everything" is more of a political stance, rather than entirely practical.