Combine the two tests folder `tests/` and `testing/`

[svij-sc]

it's a bit odd we have both tests/ and testing/ now .... there was a reason I named it testing. #185 (comment)

But it seems like that should no longer be an issue if we move testing to tests (or vise-versa).

Originally posted by @kmontemayor2-sc in #449 (comment)