Add support to run emulator for system tests.

[crwilcox]

Currently the system tests do not run with the emulator.

ERROR    grpc._plugin_wrapping:_plugin_wrapping.py:82 AuthMetadataPluginCallback "<google.auth.transport.grpc.AuthMetadataPlugin object at 0x11169b310>" raised exception!
Traceback (most recent call last):
  File "/Users/crwilcox/workspace/python-firestore/.nox/system-3-7/lib/python3.7/site-packages/grpc/_plugin_wrapping.py", line 78, in __call__
    context, _AuthMetadataPluginCallback(callback_state, callback))
  File "/Users/crwilcox/workspace/python-firestore/.nox/system-3-7/lib/python3.7/site-packages/google/auth/transport/grpc.py", line 86, in __call__
    callback(self._get_authorization_headers(context), None)
  File "/Users/crwilcox/workspace/python-firestore/.nox/system-3-7/lib/python3.7/site-packages/google/auth/transport/grpc.py", line 73, in _get_authorization_headers
    self._request, context.method_name, context.service_url, headers
  File "/Users/crwilcox/workspace/python-firestore/.nox/system-3-7/lib/python3.7/site-packages/google/auth/credentials.py", line 134, in before_request
    self.apply(headers)
  File "/Users/crwilcox/workspace/python-firestore/.nox/system-3-7/lib/python3.7/site-packages/google/auth/credentials.py", line 112, in apply
    if self.quota_project_id:
  File "/Users/crwilcox/workspace/python-firestore/.nox/system-3-7/lib/python3.7/site-packages/google/auth/credentials.py", line 83, in quota_project_id
    return self._quota_project_id
AttributeError: 'EmulatorCreds' object has no attribute '_quota_project_id'

[tseaver]

@crwilcox Did PR #402 resolve this issue?

[crwilcox]

❯ gcloud beta emulators firestore start --host-port=127.0.0.1:1234
❯ export FIRESTORE_EMULATOR_HOST=127.0.0.1:1234
❯ nox -s system-3.7

Seems mostly good locally. though some tests don't seem to work with the emulator (Partition Query)

FAILED tests/system/test_system.py::test_partition_query_no_partitions - google.api_core.exceptions.MethodNotImpl...
FAILED tests/system/test_system.py::test_partition_query - google.api_core.exceptions.MethodNotImplemented: 501 M...
FAILED tests/system/test_system.py::test_watch_query_order - assert 5 == 6
FAILED tests/system/test_system_async.py::test_partition_query_no_partitions - google.api_core.exceptions.MethodN...
FAILED tests/system/test_system_async.py::test_partition_query - google.api_core.exceptions.MethodNotImplemented:...

[tseaver]

@crwilcox

gcloud beta firestore emulator

Hmm, that doesn't work for me -- I need to run gcloud beta emulators firestore start. I'm running with updated components, I think.

And the tests don't pass at that point, either. The fail with 503 failed to connect to all addresses. Nope, I typoed the export statement.

[crwilcox]

That was a typo ;)

[tseaver]

Oddly, the systests still want a GCLOUD_PROJECT to be set in the environment, even under the emulator.