Issue #26523: The multiprocessing thread pool (multiprocessing.dummy.Pool) was untested.

Lib/test/_test_multiprocessing.py

@@ -1818,11 +1818,17 @@ class _TestPool(BaseTestCase):
                 expected_values.remove(value)
 
     def test_make_pool(self):
-        self.assertRaises(ValueError, multiprocessing.Pool, -1)
-        self.assertRaises(ValueError, multiprocessing.Pool, 0)
+        expected_error = (RemoteError if self.TYPE == 'manager'
+                          else ValueError)
 
-        p = multiprocessing.Pool(3)
+        self.assertRaises(expected_error, self.Pool, -1)
+        self.assertRaises(expected_error, self.Pool, 0)
+
+        if self.TYPE != 'manager':
+            p = self.Pool(3)
+            try:
                 self.assertEqual(3, len(p._pool))
+            finally:
                 p.close()
                 p.join()
 
@@ -1833,7 +1839,8 @@ class _TestPool(BaseTestCase):
         self.pool.terminate()
         join = TimingWrapper(self.pool.join)
         join()
-        self.assertLess(join.elapsed, 0.5)
+        # Sanity check the pool didn't wait for all tasks to finish
+        self.assertLess(join.elapsed, 2.0)
 
     def test_empty_iterable(self):
         # See Issue 12157
@@ -1851,7 +1858,7 @@ class _TestPool(BaseTestCase):
         if self.TYPE == 'processes':
             L = list(range(10))
             expected = [sqr(i) for i in L]
-            with multiprocessing.Pool(2) as p:
+            with self.Pool(2) as p:
                 r = p.map_async(sqr, L)
                 self.assertEqual(r.get(), expected)
             self.assertRaises(ValueError, p.map_async, sqr, L)
@@ -3834,7 +3841,7 @@ class ThreadsMixin(object):
     connection = multiprocessing.dummy.connection
     current_process = staticmethod(multiprocessing.dummy.current_process)
     active_children = staticmethod(multiprocessing.dummy.active_children)
-    Pool = staticmethod(multiprocessing.Pool)
+    Pool = staticmethod(multiprocessing.dummy.Pool)
     Pipe = staticmethod(multiprocessing.dummy.Pipe)
     Queue = staticmethod(multiprocessing.dummy.Queue)
     JoinableQueue = staticmethod(multiprocessing.dummy.JoinableQueue)

Misc/NEWS

@@ -298,6 +298,9 @@ Documentation
 Tests
 -----
 
+- Issue #26523: The multiprocessing thread pool (multiprocessing.dummy.Pool)
+  was untested.
+
 - Issue #26015: Added new tests for pickling iterators of mutable sequences.
 
 - Issue #26325: Added test.support.check_no_resource_warning() to check that