oeqa/context: Only set buffer mode for non-concurrent tests
Periodically we'd see:
NOTE: core-image-sato-1.0-r0 do_testsdk: ======================================================================
NOTE: core-image-sato-1.0-r0 do_testsdk: ERROR: broken-runner
NOTE: core-image-sato-1.0-r0 do_testsdk: ----------------------------------------------------------------------
NOTE: core-image-sato-1.0-r0 do_testsdk: testtools.testresult.real._StringException: Traceback (most recent call last):
File "/home/pokybuild/yocto-autobuilder/yocto-worker/nightly-mips/build/meta/lib/oeqa/core/utils/concurrencytest.py", line 122, in _run_test
test.run(process_result)
File "/usr/lib/python3.6/site-packages/subunit/__init__.py", line 1194, in run
protocol = TestProtocolServer(result, self._passthrough, self._forward)
File "/usr/lib/python3.6/site-packages/subunit/__init__.py", line 514, in __init__
stream = stream.buffer
AttributeError: '_io.StringIO' object has no attribute 'buffer'
which seems to occur if a result arrives before all the runner threads
have started. The runner's result handling changes sys.stdout to a buffer
temporarily which can be seen in other threads and it can sometimes fail.
Since the tests are running in a separate process we don't need this buffer
handling in the concurrent case so only set when not parallelising. The
concurrent class handle setting buffer mode internally.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
