Add unit test utilities for handling events and event logs

Base test class for event permission testing where we create
events which are available to internal and LV-EM users. Also added
a utility mixin for exposing event logs to LV-EM, since
unfortunately, it's handled differently than for superevents for
the time being.

gracedb/events/tests/mixins.py

 from __future__ import absolute_import
 import os
 
+from django.conf import settings
 from django.contrib.auth import get_user_model
+from django.contrib.auth.models import Group as AuthGroup, Permission
+from django.contrib.contenttypes.models import ContentType
 
-from ..models import Event, Group, Pipeline, Search
+from core.tests.utils import GraceDbTestBase
+from ..models import Event, Group, Pipeline, Search, Tag
+from ..permission_utils import assign_default_event_perms
+from ..views import update_event_perms_for_group
 
 UserModel = get_user_model()
 
@@ -14,7 +20,6 @@ class EventCreateMixin(object):
     def create_event(group_name, pipeline_name, search_name=None,
         user=None):
         """
-
         """
 
         # Create group, pipeline, and optionally, user
@@ -44,3 +49,43 @@ class EventCreateMixin(object):
         os.makedirs(event.datadir)
 
         return event
+
+
+class EventSetup(GraceDbTestBase, EventCreateMixin):
+    """
+    A base test class which creates events with specific
+    view permissions.
+    """
+
+    @classmethod
+    def setUpTestData(cls):
+        super(EventSetup, cls).setUpTestData()
+
+        # Create a few events
+        cls.internal_event = cls.create_event('EVENTGROUP', 'EVENTPIPELINE')
+        cls.lvem_event = cls.create_event('EVENTGROUP', 'EVENTPIPELINE')
+
+        # We need to make sure that the view_event permission exists
+        # I guess since it's part of a data migration and not actually listed
+        # in the 'Meta' class for the model, it's not preserved.
+        ct = ContentType.objects.get_for_model(Event)
+        p, _ = Permission.objects.get_or_create(codename='view_event',
+            name='Can view event', content_type=ct)
+
+        # Assign default permissions for internal group (also have to create
+        # executives group because this perm assign code is TERRIBLE)
+        execs, _ = AuthGroup.objects.get_or_create(name='executives')
+        assign_default_event_perms(cls.internal_event)
+        assign_default_event_perms(cls.lvem_event)
+
+        # Expose one to LV-EM
+        lvem_group = AuthGroup.objects.get(name=settings.LVEM_OBSERVERS_GROUP)
+        update_event_perms_for_group(cls.lvem_event, lvem_group, 'expose')
+
+
+class ExposeLogMixin(object):
+
+    @classmethod
+    def expose_log_to_lvem(cls, log):
+        lvem_tag, _ = Tag.objects.get_or_create(name='lvem')
+        log.tags.add(lvem_tag)