Expect_test_configSourceinclude Expect_test_config_types.S
with type 'a IO_flush.t = 'a
with type 'a IO_run.t = 'aFlush whatever need to be to get pending output out on file descriptor 0.
Synchronous check that there is no pending output on file description 0. With async, there is no guarantee that on the rhs of a IO.bind (flush ()) ... the output is completely flushed, that's why we need this.
upon_unreleasable_issue specifies how to deal with output that should not be released even if it is accepted (e.g. backtraces). The default is `CR.