`put_read_take` test is not being run during tests

[JordanMartinez]

While looking through AVar's test and trying them out myself, I noticed that one of the tests isn't even being run. I'm guessing that is a mistake:

• previous test
• middle test
• next test

In main, the middle one is missing

Including that test in main produces a failure

Not sure whether this is related to #9

[JordanMartinez]

The tests works if one fixes the string. Rather than foobazfoobar, it should be barfoobazfoo

[natefaubion]

Yeah, I think the string is just wrong. foobazfoobar would be the result if the put callback was called after it was taken, which is not correct. I'm not sure why it wasn't included. Maybe because it isn't an interesting test.