diff --git a/distributed/tests/test_worker_state_machine.py b/distributed/tests/test_worker_state_machine.py
index 98223e87b2..c232e2422b 100644
--- a/distributed/tests/test_worker_state_machine.py
+++ b/distributed/tests/test_worker_state_machine.py
@@ -1,14 +1,14 @@
 from __future__ import annotations
 
 import asyncio
-import subprocess
-import sys
+import gc
 from collections.abc import Iterator
 
 import pytest
 from tlz import first
 
-from distributed import Worker, wait
+import distributed.profile as profile
+from distributed import Nanny, Worker, wait
 from distributed.protocol.serialize import Serialize
 from distributed.utils import recursive_to_dict
 from distributed.utils_test import (
@@ -48,11 +48,12 @@ async def wait_for_state(key: str, state: TaskStateState, dask_worker: Worker) -
 
 @clean()
 def test_task_state_tracking():
-    x = TaskState("x")
-    assert len(TaskState._instances) == 1
-    assert first(TaskState._instances) == x
+    with clean():
+        x = TaskState("x")
+        assert len(TaskState._instances) == 1
+        assert first(TaskState._instances) == x
 
-    del x
+        del x
     assert len(TaskState._instances) == 0
 
 
@@ -689,46 +690,23 @@ async def test_missing_to_waiting(c, s, w1, w2, w3):
     await f1
 
 
-client_script = """
-from dask.distributed import Client
-from dask.distributed.worker_state_machine import TaskState
-
-
-def inc(x):
-    return x + 1
-
-
-if __name__ == "__main__":
-    with Client(processes=%s, n_workers=1) as client:
-        futs = client.map(inc, range(10))
-        red = client.submit(sum, futs)
-        f1 = client.submit(inc, red, pure=False)
-        f2 = client.submit(inc, red, pure=False)
-        f2.result()
-        del futs, red, f1, f2
-
-        def check():
-            assert not TaskState._instances, len(TaskState._instances)
+@gen_cluster(client=True, Worker=Nanny)
+async def test_task_state_instance_are_garbage_collected(c, s, a, b):
+    futs = c.map(inc, range(10))
+    red = c.submit(sum, futs)
+    f1 = c.submit(inc, red, pure=False)
+    f2 = c.submit(inc, red, pure=False)
 
-        client.run(check)
-"""
-
-
-@pytest.mark.parametrize("processes", [True, False])
-def test_task_state_instance_are_garbage_collected(processes, tmp_path):
-    with open(tmp_path / "script.py", mode="w") as f:
-        f.write(client_script % processes)
-
-    proc = subprocess.Popen(
-        [sys.executable, tmp_path / "script.py"],
-        stdout=subprocess.PIPE,
-        stderr=subprocess.PIPE,
-    )
-
-    out, err = proc.communicate()
+    async def check(dask_worker):
+        while dask_worker.tasks:
+            await asyncio.sleep(0.01)
+        with profile.lock:
+            gc.collect()
+        assert not TaskState._instances
 
-    assert not out
-    assert not err
+    await c.gather([f2, f1])
+    del futs, red, f1, f2
+    await c.run(check)
 
 
 @gen_cluster(client=True, nthreads=[("", 1)] * 3)
diff --git a/distributed/worker_state_machine.py b/distributed/worker_state_machine.py
index c76c5ef6bd..c4ee6d4c1f 100644
--- a/distributed/worker_state_machine.py
+++ b/distributed/worker_state_machine.py
@@ -3002,6 +3002,11 @@ def validate_state(self) -> None:
         if self.transition_counter_max:
             assert self.transition_counter < self.transition_counter_max
 
+        # Test that there aren't multiple TaskState objects with the same key in data_needed
+        assert len({ts.key for ts in self.data_needed}) == len(self.data_needed)
+        for tss in self.data_needed_per_worker.values():
+            assert len({ts.key for ts in tss}) == len(tss)
+
 
 class BaseWorker(abc.ABC):
     """Wrapper around the :class:`WorkerState` that implements instructions handling.