- apply suggestions

cou/apps/base.py

@@ -654,6 +654,9 @@ def _get_upgrade_charm_step(self, target: OpenStackRelease) -> UpgradeStep:
             logger.debug("%s channel already set to %s", self.name, self.channel)
             return UpgradeStep()
 
+        # Normally, prior the upgrade the channel is equal to the application release.
+        # However, when colocated with other app, the channel can be in a release lesser than the
+        # workload version of the application.
         if self.channel_o7k_release <= self.o7k_release:
             return UpgradeStep(
                 description=f"Upgrade '{self.name}' from '{channel}' to the new channel: "
@@ -663,7 +666,7 @@ def _get_upgrade_charm_step(self, target: OpenStackRelease) -> UpgradeStep:
 
         raise ApplicationError(
             f"The '{self.name}' application is using channel '{self.channel}'. Channels supported "
-            f"this transition: '{self.expected_current_channel(target)}', "
+            f"during this transition: '{self.expected_current_channel(target)}', "
             f"'{self.target_channel(target)}'. Manual intervention is required."
         )
 

tests/unit/apps/test_auxiliary.py

@@ -1475,8 +1475,9 @@ def test_auxiliary_wrong_channel(model):
     # or pacific. The user will need manual intervention
 
     exp_msg = (
-        r"^The 'ceph-mon' application is using channel 'quincy/stable'\. Channels supported this "
-        r"transition: '(octopus/stable)', '(octopus/stable)'\. Manual intervention is required\.$"
+        r"^The 'ceph-mon' application is using channel 'quincy/stable'\. Channels supported during"
+        r" this transition: '(octopus/stable)', '(octopus/stable)'\. "
+        r"Manual intervention is required\.$"
     )
 
     with pytest.raises(ApplicationError, match=exp_msg):

tests/unit/apps/test_core.py

@@ -1075,8 +1075,9 @@ def test_core_wrong_channel(model):
     # or victoria. The user will need manual intervention
 
     exp_msg = (
-        r"^The 'keystone' application is using channel 'wallaby/stable'\. Channels supported this "
-        r"transition: '(ussuri/stable)', '(victoria/stable)'\. Manual intervention is required\.$"
+        r"^The 'keystone' application is using channel 'wallaby/stable'\. Channels supported "
+        r"during this transition: '(ussuri/stable)', '(victoria/stable)'\. "
+        r"Manual intervention is required\.$"
     )
 
     with pytest.raises(ApplicationError, match=exp_msg):