Improve test to run on macos and cover forkserver

Author: albanD

Lib/test/_test_multiprocessing.py

@@ -5421,6 +5421,24 @@ def test_preload_resources(self):
             print(err)
             self.fail("failed spawning forkserver or grandchild")
 
+    @unittest.skipIf(sys.platform == "win32", "Only Spawn on windows so no risk of mixing")
+    @only_run_in_spawn_testsuite("avoids redundant testing since we ignore the global context.")
+    def test_mixed_startmethod(self):
+        # Fork-based locks cannot be used with spawned process
+        for process_method in ["spawn", "forkserver"]:
+            queue = multiprocessing.get_context("fork").Queue()
+            p = multiprocessing.get_context(process_method).Process(target=close_queue, args=(queue,))
+            with self.assertRaisesRegex(RuntimeError, "A SemLock created in a fork"):
+                p.start()
+
+        # non-fork-based locks can be used with all other start methods
+        for queue_method in ["spawn", "forkserver"]:
+            for process_method in multiprocessing.get_all_start_methods():
+                queue = multiprocessing.get_context(queue_method).Queue()
+                p = multiprocessing.get_context(process_method).Process(target=close_queue, args=(queue,))
+                p.start()
+                p.join()
+
 
 @unittest.skipIf(sys.platform == "win32",
                  "test semantics don't make sense on Windows")
@@ -6201,9 +6219,3 @@ class SemLock(_multiprocessing.SemLock):
         name = f'test_semlock_subclass-{os.getpid()}'
         s = SemLock(1, 0, 10, name, False)
         _multiprocessing.sem_unlink(name)
-
-    def test_semlock_mixed_context(self):
-        queue = multiprocessing.get_context("fork").Queue()
-        p = multiprocessing.get_context("spawn").Process(target=close_queue, args=(queue,))
-        with self.assertRaisesRegex(RuntimeError, "A SemLock created in a fork"):
-            p.start()