Fix Typo, Update Tests to newest FactCheck

There was a typo in `context(cl.Buffer)` that caused it to fail.
I added some tests for the fix, as well.

The tests used the `throws_pred` from FactCheck which was removed in the current version.
I replaced the uses with `@fact_throws` and `@fact` which ever was appropriate.

I updated runtests.jl to run my new tests as well es existing ones from test_buffer.jl that weren't being run.