diff --git a/charms/worker/k8s/src/inspector.py b/charms/worker/k8s/src/inspector.py
index 783b5ea1..1a73b4de 100644
--- a/charms/worker/k8s/src/inspector.py
+++ b/charms/worker/k8s/src/inspector.py
@@ -44,7 +44,7 @@ def _get_client(self) -> Client:
             self.client = Client(config=config.get())
         return self.client
 
-    def get_nodes(self, labels: LabelSelector) -> Optional[List[Node]]:
+    def get_nodes(self, labels: Optional[LabelSelector] = None) -> Optional[List[Node]]:
         """Get nodes from the cluster.
 
         Args:
@@ -56,6 +56,7 @@ def get_nodes(self, labels: LabelSelector) -> Optional[List[Node]]:
         Raises:
             ClusterInspectorError: If the nodes cannot be retrieved.
         """
+        labels = labels or {}
         client = self._get_client()
         try:
 
diff --git a/charms/worker/k8s/src/upgrade.py b/charms/worker/k8s/src/upgrade.py
index f85e5122..520a1f7a 100644
--- a/charms/worker/k8s/src/upgrade.py
+++ b/charms/worker/k8s/src/upgrade.py
@@ -89,10 +89,11 @@ def pre_upgrade_check(self) -> None:
         Raises:
             ClusterNotReadyError: If the cluster is not ready for an upgrade.
         """
+        if self.charm.is_worker:
+            log.info("TODO: Find some pre-upgrade checks for worker application.")
+            return
         try:
-            nodes = self.cluster_inspector.get_nodes(
-                labels={"juju-charm": "k8s-worker" if self.charm.is_worker else "k8s"}
-            )
+            nodes = self.cluster_inspector.get_nodes()
             failing_pods = self.cluster_inspector.verify_pods_running(["kube-system"])
         except ClusterInspector.ClusterInspectorError as e:
             raise ClusterNotReadyError(
diff --git a/tests/integration/conftest.py b/tests/integration/conftest.py
index 9e269810..c55b9922 100644
--- a/tests/integration/conftest.py
+++ b/tests/integration/conftest.py
@@ -20,7 +20,7 @@
 from pytest_operator.plugin import OpsTest
 
 from .cos_substrate import LXDSubstrate
-from .helpers import Bundle, Charm, cloud_type, get_unit_cidrs, is_deployed
+from .helpers import Bundle, CharmUrl, cloud_type, get_unit_cidrs, is_deployed
 
 log = logging.getLogger(__name__)
 TEST_DATA = Path(__file__).parent / "data"
@@ -72,7 +72,8 @@ def pytest_configure(config):
     config.addinivalue_line("markers", "cos: mark COS integration tests.")
     config.addinivalue_line(
         "markers",
-        "bundle(file='', apps_local={}, apps_channel={}, apps_resources={}): specify a YAML bundle file for a test.",
+        "bundle(file='', apps_local={}, apps_channel={}, apps_resources={}): "
+        "specify a YAML bundle file for a test.",
     )
 
 
@@ -202,7 +203,7 @@ async def grafana_agent(kubernetes_cluster: Model):
     machine_series = juju.utils.get_version_series(data["base"].split("@")[1])
 
     await kubernetes_cluster.deploy(
-        Charm.craft_url("grafana-agent", machine_series, machine_arch),
+        str(CharmUrl.craft("grafana-agent", machine_series, machine_arch)),
         channel="stable",
         series=machine_series,
     )
diff --git a/tests/integration/helpers.py b/tests/integration/helpers.py
index 97819d00..03a22054 100644
--- a/tests/integration/helpers.py
+++ b/tests/integration/helpers.py
@@ -14,7 +14,7 @@
 from functools import cache, cached_property
 from itertools import chain
 from pathlib import Path
-from typing import Dict, List, Mapping, Optional, Sequence, Tuple
+from typing import Dict, List, Mapping, Optional, Tuple
 
 import yaml
 from juju import unit
@@ -326,6 +326,7 @@ def find(cls, name: str) -> Optional["Charm"]:
         """
         if charmcraft := CHARMCRAFT_DIRS.get(name):
             return cls(charmcraft)
+        return None
 
     async def resolve(self, ops_test: OpsTest, arch: str) -> "Charm":
         """Build or find the charm with ops_test.
@@ -440,7 +441,6 @@ async def discover_charm_files(self, ops_test: OpsTest) -> Dict[str, Charm]:
 
         Args:
             ops_test: Instance of the pytest-operator plugin
-            arch: Cloud architecture
 
         Returns:
             Mapping: application name to Charm object
@@ -457,6 +457,7 @@ async def apply_marking(self, ops_test: OpsTest, markings: Markings):
 
         Args:
             ops_test: Instance of the pytest-operator plugin
+            markings: Markings from the test
         """
         _type, _vms = await cloud_type(ops_test)
         if _type == "lxd" and not _vms:
@@ -496,7 +497,7 @@ def switch(
             resources (dict): Optional resources to add
 
         Raises:
-            ValueError: if both path and channel are provided, or neither are provided
+            FileNotFoundError: if the local charm file is not found
         """
         app = self.applications.get(name)
         if not app:
diff --git a/tests/integration/test_upgrade.py b/tests/integration/test_upgrade.py
index 1d22c9e1..55f5ddb8 100644
--- a/tests/integration/test_upgrade.py
+++ b/tests/integration/test_upgrade.py
@@ -15,7 +15,7 @@
 import yaml
 from pytest_operator.plugin import OpsTest
 
-from .helpers import Bundle, Charm, get_leader
+from .helpers import Bundle, get_leader
 
 # This pytest mark configures the test environment to use the Canonical Kubernetes
 # deploying charms from the edge channels, then upgrading them to the built charm.
@@ -53,7 +53,7 @@ async def _refresh(app_name: str):
         app: Optional[juju.application.Application] = kubernetes_cluster.applications[app_name]
         assert app is not None, f"Application {app_name} not found"
 
-        log.info(f"Refreshing {app_name}")
+        log.info("Refreshing %s", app_name)
         leader_idx: int = await get_leader(app)
         leader: juju.unit.Unit = app.units[leader_idx]
         action = await leader.run_action("pre-upgrade-check")