diff --git a/cardano_node_tests/utils/parallel_run.py b/cardano_node_tests/utils/parallel_run.py
index 22a5f155c..efe484ae6 100644
--- a/cardano_node_tests/utils/parallel_run.py
+++ b/cardano_node_tests/utils/parallel_run.py
@@ -21,8 +21,8 @@
 LOCK_LOG_FILE = ".lock.log"
 SESSION_RUNNING_FILE = ".session_running"
 TEST_SINGLETON_FILE = ".test_singleton"
-RESOURCE_LOCKED = ".resource_locked"
-RESOURCE_IN_USE = ".resource_in_use"
+RESOURCE_LOCKED_GLOB = ".resource_locked"
+RESOURCE_IN_USE_GLOB = ".resource_in_use"
 RESTART_NEEDED_GLOB = ".needs_restart"
 RESTART_IN_PROGRESS_GLOB = ".restart_in_progress"
 RESTART_AFTER_MARK_GLOB = ".restart_after_mark"
@@ -74,12 +74,14 @@ def cache(self) -> ClusterManagerCache:
         return self.get_cache()
 
     def _log(self, msg: str) -> None:
+        """Log message - needs to be called while having lock."""
         if not self.lock_log:
             return
         with open(self.lock_log, "a") as logfile:
             logfile.write(f"{datetime.datetime.now()} on {self.worker_id}: {msg}\n")
 
     def _locked_log(self, msg: str) -> None:
+        """Log message - will obtain lock first."""
         if not self.lock_log:
             return
         with helpers.FileLockIfXdist(self.cluster_lock):
@@ -187,14 +189,14 @@ def on_test_stop(self) -> None:
 
             # remove resource locking files created by the worker
             resource_locking_files = list(
-                self.lock_dir.glob(f"{RESOURCE_LOCKED}_*_{self.worker_id}")
+                self.lock_dir.glob(f"{RESOURCE_LOCKED_GLOB}_*_{self.worker_id}")
             )
             for f in resource_locking_files:
                 os.remove(f)
 
             # remove "resource in use" files created by the worker
             resource_in_use_files = list(
-                self.lock_dir.glob(f"{RESOURCE_IN_USE}_*_{self.worker_id}")
+                self.lock_dir.glob(f"{RESOURCE_IN_USE_GLOB}_*_{self.worker_id}")
             )
             for f in resource_in_use_files:
                 os.remove(f)
@@ -216,6 +218,11 @@ def get(  # noqa: C901
         use_resources: UnpackableSequence = (),
         cleanup: bool = False,
     ) -> clusterlib.ClusterLib:
+        """Return the `clusterlib.ClusterLib` instance once we can start the test.
+
+        It checks current conditions and waits if the conditions don't allow to start the test
+        right away.
+        """
         # pylint: disable=too-many-statements,too-many-branches
         restart_here = False
         mark_start_here = False
@@ -225,6 +232,7 @@ def get(  # noqa: C901
         test_running_file = self.lock_dir / f"{TEST_RUNNING_GLOB}_{self.worker_id}"
         cluster_obj = self.cache.cluster_obj
 
+        # iterate until it is possible to start the test
         while True:
             if not first_iteration:
                 helpers.xdist_sleep(random.random() * sleep_delay)
@@ -352,11 +360,11 @@ def get(  # noqa: C901
                 if lock_resources:
                     res_usable = False
                     for res in lock_resources:
-                        res_locked = list(self.lock_dir.glob(f"{RESOURCE_LOCKED}_{res}_*"))
+                        res_locked = list(self.lock_dir.glob(f"{RESOURCE_LOCKED_GLOB}_{res}_*"))
                         if res_locked:
                             self._log(f"resource '{res}' locked, cannot start")
                             break
-                        res_used = list(self.lock_dir.glob(f"{RESOURCE_IN_USE}_{res}_*"))
+                        res_used = list(self.lock_dir.glob(f"{RESOURCE_IN_USE_GLOB}_{res}_*"))
                         if res_used:
                             self._log(f"resource '{res}' in use, cannot lock and start")
                             break
@@ -372,19 +380,23 @@ def get(  # noqa: C901
                         "starting and locking"
                     )
 
+                    # create status file for each locked resource
                     _ = [
-                        open(self.lock_dir / f"{RESOURCE_LOCKED}_{r}_{self.worker_id}", "a").close()
+                        open(
+                            self.lock_dir / f"{RESOURCE_LOCKED_GLOB}_{r}_{self.worker_id}", "a"
+                        ).close()
                         for r in lock_resources
                     ]
 
                 # filter out `lock_resources` from the list of `use_resources`
-                use_resources = list(set(use_resources) - set(lock_resources))
+                if use_resources and lock_resources:
+                    use_resources = list(set(use_resources) - set(lock_resources))
 
                 # this test wants to use some resources, check if these are not locked
                 if use_resources:
                     res_locked = []
                     for res in use_resources:
-                        res_locked = list(self.lock_dir.glob(f"{RESOURCE_LOCKED}_{res}_*"))
+                        res_locked = list(self.lock_dir.glob(f"{RESOURCE_LOCKED_GLOB}_{res}_*"))
                         if res_locked:
                             self._log(f"resource '{res}' locked, cannot start")
                             break
@@ -393,8 +405,12 @@ def get(  # noqa: C901
                         no_tests_iteration = 0
                         continue
                     self._log("none of the resources in '{use_resources}' locked, starting")
+
+                    # create status file for each in-use resource
                     _ = [
-                        open(self.lock_dir / f"{RESOURCE_IN_USE}_{r}_{self.worker_id}", "a").close()
+                        open(
+                            self.lock_dir / f"{RESOURCE_IN_USE_GLOB}_{r}_{self.worker_id}", "a"
+                        ).close()
                         for r in use_resources
                     ]
 
@@ -430,6 +446,7 @@ def get(  # noqa: C901
                 if not cluster_obj:
                     cluster_obj = clusterlib.ClusterLib(state_dir)
 
+                # `cluster_obj` is ready, we can start the test
                 break
 
         return cluster_obj