chore: new owl bot post processor docker image (#70)

gcr.io/repo-automation-bots/owlbot-python:latest@sha256:457583330eec64daa02aeb7a72a04d33e7be2428f646671ce4045dcbc0191b1e

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

packages/google-cloud-billing/.github/.OwlBot.lock.yaml

@@ -1,4 +1,3 @@
 docker:
-  digest: sha256:cfc0e802701262c211703c468874d767f65dabe6a1a71d0e07bfc8a3d5175f32
   image: gcr.io/repo-automation-bots/owlbot-python:latest
-
+  digest: sha256:457583330eec64daa02aeb7a72a04d33e7be2428f646671ce4045dcbc0191b1e

packages/google-cloud-billing/.pre-commit-config.yaml

@@ -26,6 +26,6 @@ repos:
     hooks:
     - id: black
 -   repo: https://gitlab.com/pycqa/flake8
-    rev: 3.9.0
+    rev: 3.9.1
     hooks:
     - id: flake8

packages/google-cloud-billing/CONTRIBUTING.rst

@@ -160,21 +160,7 @@ Running System Tests
   auth settings and change some configuration in your project to
   run all the tests.
 
-- System tests will be run against an actual project and
-  so you'll need to provide some environment variables to facilitate
-  authentication to your project:
-
-  - ``GOOGLE_APPLICATION_CREDENTIALS``: The path to a JSON key file;
-    Such a file can be downloaded directly from the developer's console by clicking
-    "Generate new JSON key". See private key
-    `docs <https://cloud.google.com/storage/docs/authentication#generating-a-private-key>`__
-    for more details.
-
-- Once you have downloaded your json keys, set the environment variable 
-  ``GOOGLE_APPLICATION_CREDENTIALS`` to the absolute path of the json file::
-
-   $ export GOOGLE_APPLICATION_CREDENTIALS="/Users/<your_username>/path/to/app_credentials.json"
-
+- System tests will be run against an actual project. You should use local credentials from gcloud when possible. See `Best practices for application authentication <https://cloud.google.com/docs/authentication/best-practices-applications#local_development_and_testing_with_the>`__. Some tests require a service account. For those tests see `Authenticating as a service account <https://cloud.google.com/docs/authentication/production>`__.
 
 *************
 Test Coverage

packages/google-cloud-billing/noxfile.py

@@ -62,16 +62,9 @@ def lint(session):
     session.run("flake8", "google", "tests")
 
 
-@nox.session(python="3.6")
+@nox.session(python=DEFAULT_PYTHON_VERSION)
 def blacken(session):
-    """Run black.
-
-    Format code to uniform standard.
-
-    This currently uses Python 3.6 due to the automated Kokoro run of synthtool.
-    That run uses an image that doesn't have 3.6 installed. Before updating this
-    check the state of the `gcp_ubuntu_config` we use for that Kokoro run.
-    """
+    """Run black. Format code to uniform standard."""
     session.install(BLACK_VERSION)
     session.run(
         "black", *BLACK_PATHS,
@@ -131,9 +124,6 @@ def system(session):
     # Check the value of `RUN_SYSTEM_TESTS` env var. It defaults to true.
     if os.environ.get("RUN_SYSTEM_TESTS", "true") == "false":
         session.skip("RUN_SYSTEM_TESTS is set to false, skipping")
-    # Sanity check: Only run tests if the environment variable is set.
-    if not os.environ.get("GOOGLE_APPLICATION_CREDENTIALS", ""):
-        session.skip("Credentials must be set via environment variable")
     # Install pyopenssl for mTLS testing.
     if os.environ.get("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false") == "true":
         session.install("pyopenssl")