for testing purposes

[parthea]

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Fixes #<issue_number_goes_here> 🦕

[busunkim96]

It looks like the sample that is failing is the one that exercises the mapping field:

python-video-transcoder/samples/snippets/create_job_with_standalone_captions.py

Lines 83 to 110 in c14695b

	transcoder_v1.types.ElementaryStream(
	key="vtt-stream0",
	# The following doesn't work because "mapping" is a reserved
	# argument name in GCP python client libraries (see
	# https://github.com/googleapis/proto-plus-python/blob/main/proto/message.py#L447):
	#
	# text_stream=transcoder_v1.types.TextStream(
	# codec="webvtt",
	# mapping=[
	# transcoder_v1.types.TextStream.TextMapping(
	# atom_key="atom0",
	# input_key="caption-input0",
	# input_track=0,
	# ),
	# ],
	# ),
	# Use a python dictionary as a workaround:
	text_stream={
	"codec": "webvtt",
	"mapping": [
	{
	"atom_key": "atom0",
	"input_key": "caption-input0",
	"input_track": 0,
	}
	],
	},
	),

capsys = <_pytest.capture.CaptureFixture object at 0x7f4e4e1e1b50>
test_bucket = <Bucket: python-samples-transcoder-010b96db-c2a2-4939-b543-748a4be90aa8>

    def test_create_job_with_embedded_captions(capsys, test_bucket):
        create_job_with_embedded_captions.create_job_with_embedded_captions(
>           project_id, location, input_uri, captions_uri, output_uri_for_embedded_captions,
        )

job_test.py:410:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
create_job_with_embedded_captions.py:105: in create_job_with_embedded_captions
    "input_track": 0,
.nox/py-3-7/lib/python3.7/site-packages/proto/message.py:548: in __init__
    pb_value = marshal.to_proto(pb_type, value)
.nox/py-3-7/lib/python3.7/site-packages/proto/marshal/marshal.py:211: in to_proto
    pb_value = rule.to_proto(value)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <proto.marshal.rules.message.MessageRule object at 0x7f4e50560490>
value = {'codec': 'cea608', 'mapping': [{'atom_key': 'atom0', 'input_key': 'caption-input0', 'input_track': 0}]}

    def to_proto(self, value):
        if isinstance(value, self._wrapper):
            return self._wrapper.pb(value)
        if isinstance(value, dict) and not self.is_map:
            # We need to use the wrapper's marshaling to handle
            # potentially problematic nested messages.
            try:
                # Try the fast path first.
>               return self._descriptor(**value)
E               ValueError: Protocol message TextStream has no "mapping" field.

.nox/py-3-7/lib/python3.7/site-packages/proto/marshal/rules/message.py:36: ValueError

[parthea]

I wasn't able to produce this initially. I think there was an issue where my environment. This issue will be fixed in googleapis/proto-plus-python#301.