test: add tests for clearBuffer state machine
Checklist
-
make -j8 test
(UNIX), orvcbuild test nosign
(Windows) passes -
tests and/or benchmarks are included -
commit message follows commit guidelines
Affected core subsystem(s)
stream, test
Description of change
This checks to see that clearBuffer appropriately decrements the correct values in _writableState when clearBuffer is invoked in end.
Closes #8687 (closed).