isn't this the 2nd output?

isn't this the third output?

same question as above -- what is outputs[0] ?

so we have partial.slp.test.ts and also partial.test.slp.ts ?

I can't really tell from the naming what I should expect to find in each file / why they are distinct.

yeah well the OP_RETURN is the 0th output 🙃

You would've hoped there's a convention for this already, but I can change it for clarity

outputs[0] is the OP_RETURN
I can add a test that checks if its Script starts with OP_RETURN "SLP\0" if that helps :)

Good point—maybe call it partial-helpers-slp.ts, or something else

I think the else has two good reasons:

1. If a user specifies something other than ONESHOT and PARTIAL they should get an error (instead of falling into PARTIAL by default)
2. If we add another variant, we can simply add another else if branch

same reason here