It's not a question of wether something might break, it's a question of when will it break and how long a new introduced bug might be undetcted, that could have easily detected by some tests? Bugs always happen in projects, if someone says otherwise, he either proved his program to be correct (e.g. in COQ) or is wrong (and sometimes both :).

In that case, I wouldn't. But I believe that it will happen eventually, this is not a 10lines project, has many lines of code and since it's new, I expect a lot to be changed. Then those changes are going to break features.

If you are worried about them breaking it as they develop it, but like the current implementation then just use the current implementation.

If you feel like having tests are a blocking feature for you then just watch this issue: https://github.com/frappe/charts/issues/7