Use pendulum for datetime operations when possible

Currently, we use both Python's built-in datetime library and Pendulum
to do datetime operations. For the sake of consistency, we should try to
stick to one library for datetimes. We could have used either, but
Pendulum has a more ergonomic API, so I decided to go with it when
possible.

The places where were we didn't / couldn't replace datetime are:
- checking instances of datetimes. Pendulum's objects are subclasses of
  python native datetime objects, so it's still useful to import
  datetime in those cases of using is_instance()
- WTForms date validators expect datetime style string formats --
  Pendulum has its own format for formatting/ parsing strings. As such,
  our custom validator DateRange needs to use datetime.stptime() to
  account for this format.

tests/models/test_application_role.py

@@ -1,4 +1,5 @@
 import pytest
+import pendulum
 
 from atst.domain.permission_sets import PermissionSets
 from atst.domain.environment_roles import EnvironmentRoles
@@ -61,7 +62,7 @@ def test_environment_roles():
 
 
 def test_display_status():
-    yesterday = datetime.date.today() - datetime.timedelta(days=1)
+    yesterday = pendulum.today().subtract(days=1)
     expired_invite = ApplicationInvitationFactory.create(expiration_time=yesterday)
     assert expired_invite.role.display_status == "invite_expired"
 

tests/models/test_portfolio.py

@@ -6,7 +6,6 @@ from tests.factories import (
     random_future_date,
     random_past_date,
 )
-import datetime
 import pendulum
 from decimal import Decimal
 import pytest
@@ -83,7 +82,7 @@ def test_funding_duration(session):
         portfolio=portfolio,
         signed_at=random_past_date(),
         create_clins=[
-            {"start_date": datetime.datetime.now(), "end_date": funding_end_date,}
+            {"start_date": pendulum.now(tz="utc"), "end_date": funding_end_date,}
         ],
     )
 
@@ -106,7 +105,7 @@ def test_days_remaining(session):
 
     assert (
         portfolio.days_to_funding_expiration
-        == (funding_end_date - datetime.date.today()).days
+        == (funding_end_date - pendulum.today()).days
     )
 
     # empty portfolio
@@ -121,8 +120,8 @@ def test_active_task_orders(session):
         signed_at=random_past_date(),
         create_clins=[
             {
-                "start_date": datetime.date(2019, 1, 1),
-                "end_date": datetime.date(2019, 10, 31),
+                "start_date": pendulum.date(2019, 1, 1),
+                "end_date": pendulum.date(2019, 10, 31),
             }
         ],
     )

tests/models/test_portfolio_invitations.py

@@ -1,4 +1,4 @@
-import datetime
+import pendulum
 
 from atst.models import InvitationStatus, PortfolioRoleStatus
 
@@ -17,7 +17,7 @@ def test_expired_invite_is_not_revokable():
         portfolio=portfolio, user=user, status=PortfolioRoleStatus.PENDING
     )
     invite = PortfolioInvitationFactory.create(
-        expiration_time=datetime.datetime.now() - datetime.timedelta(minutes=60),
+        expiration_time=pendulum.now(tz="utc").subtract(minutes=60),
         role=portfolio_role,
     )
     assert not invite.is_revokable

tests/models/test_portfolio_role.py

@@ -1,5 +1,5 @@
 import pytest
-import datetime
+import pendulum
 
 from atst.domain.environments import Environments
 from atst.domain.portfolios import Portfolios
@@ -204,7 +204,7 @@ def test_status_when_invitation_is_expired():
     PortfolioInvitationFactory.create(
         role=portfolio_role,
         status=InvitationStatus.PENDING,
-        expiration_time=datetime.datetime.now() - datetime.timedelta(seconds=1),
+        expiration_time=pendulum.now(tz="utc").subtract(seconds=1),
     )
     assert portfolio_role.display_status == "invite_expired"
 

tests/models/test_task_order.py

@@ -1,6 +1,6 @@
 from werkzeug.datastructures import FileStorage
 import pytest
-from datetime import date
+import pendulum
 from unittest.mock import patch, PropertyMock
 import pendulum
 
@@ -13,11 +13,11 @@ from tests.mocks import PDF_FILENAME
 
 
 def test_period_of_performance_is_first_to_last_clin():
-    start_date = date(2019, 6, 6)
-    end_date = date(2020, 6, 6)
+    start_date = pendulum.date(2019, 6, 6)
+    end_date = pendulum.date(2020, 6, 6)
 
-    intermediate_start_date = date(2019, 7, 1)
-    intermediate_end_date = date(2020, 3, 1)
+    intermediate_start_date = pendulum.date(2019, 7, 1)
+    intermediate_end_date = pendulum.date(2020, 3, 1)
 
     task_order = TaskOrderFactory.create(
         clins=[

tests/models/test_user.py

@@ -1,6 +1,6 @@
 import pytest
 from sqlalchemy.exc import InternalError
-from datetime import datetime
+import pendulum
 
 from atst.database import db
 from atst.domain.users import Users
@@ -44,7 +44,7 @@ def test_deleted_application_roles_are_ignored(session):
 
 def test_does_not_log_user_update_when_updating_last_login(mock_logger):
     user = UserFactory.create()
-    user.last_login = datetime.now()
+    user.last_login = pendulum.now(tz="utc")
     db.session.add(user)
     db.session.commit()
     assert "Audit Event update" not in mock_logger.messages