[3.9] bpo-45209: fix UserWarning: resource_tracker in test_multiprocessing (GH-28377)

Lib/test/_test_multiprocessing.py

@@ -4147,6 +4147,13 @@ def test_shared_memory_cleaned_after_process_termination(self):
                                      " a process was abruptly terminated.")
 
             if os.name == 'posix':
+                # Without this line it was raising warnings like:
+                #   UserWarning: resource_tracker:
+                #   There appear to be 1 leaked shared_memory
+                #   objects to clean up at shutdown
+                # See: https://bugs.python.org/issue45209
+                resource_tracker.unregister(f"/{name}", "shared_memory")
+
                 # A warning was emitted by the subprocess' own
                 # resource_tracker (on Windows, shared memory segments
                 # are released automatically by the OS).

Misc/NEWS.d/next/Tests/2021-09-15-23-32-39.bpo-45209.55ntL5.rst

@@ -0,0 +1,2 @@
+Fix ``UserWarning: resource_tracker`` warning in
+``_test_multiprocessing._TestSharedMemory.test_shared_memory_cleaned_after_process_termination``