Add more tests of readUntil
Add more tests of readUntil

To more tightly specify the behavior of the until function.

Note:  The "return 0" test currently fails.  I'm reconsidering what to
do for this case.

Signed-off-by: Kevin Locke <ffb4761cba839470133bee36aeb139f58d7dbaa9@kevinlocke.name>

kevinoid/promised-read,kevinoid/promised-read,kevinoid/promised-read