tests/RingBuffer: rename fillTestBuffer to testFillBuffer.

Make it a test as well.
tests/RingBuffer: s/total/putTotal/; s/readTotal/getTotal/; check .isFull

The check for isFull was to get it to cease looping when the buffer is
full even when <- somehow returns true when it shouldn't. After that,
it should fail the assertions following the loop.
tests/RingBuffer: add limit to number of puts.

If buffer<-i counts past the capacity of the buffer, fail an assertion.
This behavior should be impossible.
RingBuffer: Adjust queue<-elem operator precedence.

Use a precedence between a comparative and a cast. This allows
expressions like `!buffer.isFull && buffer <- E` or vice versa (swap
expressions on each side of the conjunction) to work.