Thoughts
The thing I don't like about writing tests for code is that it's really hard to write good tests and too easy to give yourself a false
sense of confidence.
If there's an edge case you're forgetting about, you can write 10 tests covering basic cases
```
assert(sum(1) === 1)
assert(sum(1, 2) === 3)
assert(sum(1, 2, 3) === 6)
```
And that tells you nothing about the behavior if the last element is `NaN`.
And if you think, "oh I wonder if this works with `NaN`" you can try it or look at your code without importing a testing framework. The hard part about avoiding bugs is predicting the edge cases, not testing if it works in the edge cases.
I don't know, I don't get it.