test(translation): add VPC-SC system tests

[pkumusic]

No description provided.

[busunkim96]

Thank you for making the updates!

The build should turn green once you run the code formatter: nox -s blacken from the translate/ directory.

If you do not have nox installed, you can get it with python3 -m pip install nox.

[busunkim96]

There are a few more linter errors:

flake8 google tests
tests/system/test_vpcsc.py:23:1: F401 'google.cloud.translate_v3beta1.proto.translation_service_pb2' imported but unused
tests/system/test_vpcsc.py:24:1: F401 'google.longrunning.operations_pb2' imported but unused
tests/system/test_vpcsc.py:85:9: E731 do not assign a lambda expression, use a def
tests/system/test_vpcsc.py:90:9: E731 do not assign a lambda expression, use a def
tests/system/test_vpcsc.py:102:9: E731 do not assign a lambda expression, use a def
tests/system/test_vpcsc.py:105:9: E731 do not assign a lambda expression, use a def
tests/system/test_vpcsc.py:115:9: E731 do not assign a lambda expression, use a def
tests/system/test_vpcsc.py:116:9: E731 do not assign a lambda expression, use a def
tests/system/test_vpcsc.py:124:9: E731 do not assign a lambda expression, use a def
tests/system/test_vpcsc.py:127:9: E731 do not assign a lambda expression, use a def
tests/system/test_vpcsc.py:143:9: E731 do not assign a lambda expression, use a def
tests/system/test_vpcsc.py:150:9: E731 do not assign a lambda expression, use a def

[pkumusic]

Hi Bu Sun, looks like all checks passed. Can we merge the pull requests?

Best,
Music