chore: blacken (#375)

diff --git a/system_tests/conftest.py b/system_tests/conftest.py
index d0f7cc0..3f089c4 100644
--- a/system_tests/conftest.py
+++ b/system_tests/conftest.py
@@ -24,13 +24,13 @@
 
 
 HERE = os.path.dirname(__file__)
-DATA_DIR = os.path.join(HERE, 'data')
-SERVICE_ACCOUNT_FILE = os.path.join(DATA_DIR, 'service_account.json')
-AUTHORIZED_USER_FILE = os.path.join(DATA_DIR, 'authorized_user.json')
+DATA_DIR = os.path.join(HERE, "data")
+SERVICE_ACCOUNT_FILE = os.path.join(DATA_DIR, "service_account.json")
+AUTHORIZED_USER_FILE = os.path.join(DATA_DIR, "authorized_user.json")
 URLLIB3_HTTP = urllib3.PoolManager(retries=False)
 REQUESTS_SESSION = requests.Session()
 REQUESTS_SESSION.verify = False
-TOKEN_INFO_URL = 'https://www.googleapis.com/oauth2/v3/tokeninfo'
+TOKEN_INFO_URL = "https://www.googleapis.com/oauth2/v3/tokeninfo"
 
 
 @pytest.fixture
@@ -45,33 +45,34 @@
     yield AUTHORIZED_USER_FILE
 
 
-@pytest.fixture(params=['urllib3', 'requests'])
+@pytest.fixture(params=["urllib3", "requests"])
 def http_request(request):
     """A transport.request object."""
-    if request.param == 'urllib3':
+    if request.param == "urllib3":
         yield google.auth.transport.urllib3.Request(URLLIB3_HTTP)
-    elif request.param == 'requests':
+    elif request.param == "requests":
         yield google.auth.transport.requests.Request(REQUESTS_SESSION)
 
 
 @pytest.fixture
 def token_info(http_request):
     """Returns a function that obtains OAuth2 token info."""
+
     def _token_info(access_token=None, id_token=None):
         query_params = {}
 
         if access_token is not None:
-            query_params['access_token'] = access_token
+            query_params["access_token"] = access_token
         elif id_token is not None:
-            query_params['id_token'] = id_token
+            query_params["id_token"] = id_token
         else:
-            raise ValueError('No token specified.')
+            raise ValueError("No token specified.")
 
         url = _helpers.update_query(TOKEN_INFO_URL, query_params)
 
-        response = http_request(url=url, method='GET')
+        response = http_request(url=url, method="GET")
 
-        return json.loads(response.data.decode('utf-8'))
+        return json.loads(response.data.decode("utf-8"))
 
     yield _token_info
 
@@ -79,9 +80,10 @@
 @pytest.fixture
 def verify_refresh(http_request):
     """Returns a function that verifies that credentials can be refreshed."""
+
     def _verify_refresh(credentials):
         if credentials.requires_scopes:
-            credentials = credentials.with_scopes(['email', 'profile'])
+            credentials = credentials.with_scopes(["email", "profile"])
 
         credentials.refresh(http_request)
 
@@ -95,8 +97,9 @@
     """Checks to make sure that requisite data files are available."""
     if not os.path.isdir(DATA_DIR):
         raise EnvironmentError(
-            'In order to run system tests, test data must exist in '
-            'system_tests/data. See CONTRIBUTING.rst for details.')
+            "In order to run system tests, test data must exist in "
+            "system_tests/data. See CONTRIBUTING.rst for details."
+        )
 
 
 def pytest_configure(config):