For https://github.com/GoogleCloudPlatform/google-cloud-python/pull/3674

gistfile1.txt

$ cd datastore/
$ # modify nox.py to allow posargs
$ # modify google/cloud/datastore/client.py to make `_datastore_api()`
$ #      its return value
$ nox -s system_tests -- -s
nox > Running session system_tests(python_version='2.7')
nox > virtualenv /home/dhermes/google_contracting/foog/datastore/.nox/sys-2-7 -p python2.7
nox > chdir /home/dhermes/google_contracting/foog/datastore
nox > pip install --upgrade mock pytest ../core/
nox > pip install --upgrade ../test_utils/
nox > pip install --upgrade .
nox > py.test --quiet tests/system -s
<google.cloud.datastore._http.HTTPDatastoreAPI object at 0x7f7ebf40c610>
...
<google.cloud.datastore._http.HTTPDatastoreAPI object at 0x7f7ebf40c610>
.<google.cloud.datastore._http.HTTPDatastoreAPI object at 0x7f7ebf40c610>
<google.cloud.datastore._http.HTTPDatastoreAPI object at 0x7f7ebf40c610>

21 passed in 9.18 seconds
nox > Session system_tests(python_version='2.7') successful. :)
nox > Running session system_tests(python_version='3.6')
nox > virtualenv /home/dhermes/google_contracting/foog/datastore/.nox/sys-3-6 -p python3.6
nox > chdir /home/dhermes/google_contracting/foog/datastore
nox > pip install --upgrade mock pytest ../core/
nox > pip install --upgrade ../test_utils/
nox > pip install --upgrade .
nox > py.test --quiet tests/system -s
<google.cloud.datastore._http.HTTPDatastoreAPI object at 0x7f02a2e4e2b0>
...
.<google.cloud.datastore._http.HTTPDatastoreAPI object at 0x7f02a2e4e2b0>
<google.cloud.datastore._http.HTTPDatastoreAPI object at 0x7f02a2e4e2b0>

21 passed in 9.60 seconds
nox > Session system_tests(python_version='3.6') successful. :)
nox > Ran multiple sessions:
nox > * system_tests(python_version='2.7'): passed
nox > * system_tests(python_version='3.6'): passed