Issue #21755: Skip {Frozen,Source}_DeadlockAvoidanceTests tests when

Python is built without threads.

Lib/test/test_importlib/test_locks.py

@@ -52,8 +52,8 @@ else:
         pass
 
 
-@unittest.skipUnless(threading, "threads needed for this test")
-class DeadlockAvoidanceTests:
+if threading is not None:
+    class DeadlockAvoidanceTests:
 
         def setUp(self):
             try:
@@ -76,14 +76,17 @@ class DeadlockAvoidanceTests:
                 NTHREADS = NLOCKS - 1
             barrier = threading.Barrier(NTHREADS)
             results = []
+
             def _acquire(lock):
-            """Try to acquire the lock. Return True on success, False on deadlock."""
+                """Try to acquire the lock. Return True on success,
+                False on deadlock."""
                 try:
                     lock.acquire()
                 except self.DeadlockError:
                     return False
                 else:
                     return True
+
             def f():
                 a, b = pairs.pop()
                 ra = _acquire(a)
@@ -113,13 +116,22 @@ class DeadlockAvoidanceTests:
             self.assertEqual(results.count((True, True)), len(results))
 
 
-DEADLOCK_ERRORS = {kind: splitinit._bootstrap._DeadlockError
+    DEADLOCK_ERRORS = {kind: splitinit._bootstrap._DeadlockError
                        for kind, splitinit in init.items()}
 
-(Frozen_DeadlockAvoidanceTests,
+    (Frozen_DeadlockAvoidanceTests,
      Source_DeadlockAvoidanceTests
      ) = test_util.test_both(DeadlockAvoidanceTests,
-                         LockType=LOCK_TYPES, DeadlockError=DEADLOCK_ERRORS)
+                             LockType=LOCK_TYPES,
+                             DeadlockError=DEADLOCK_ERRORS)
+else:
+    DEADLOCK_ERRORS = {}
+
+    class Frozen_DeadlockAvoidanceTests(unittest.TestCase):
+        pass
+
+    class Source_DeadlockAvoidanceTests(unittest.TestCase):
+        pass
 
 
 class LifetimeTests: