Issue #12981: test_multiprocessing: catch ImportError when importing

multiprocessing.reduction, which may not be available (e.g. if the OS doesn't
support FD passing over Unix domain sockets).

Lib/test/test_multiprocessing.py

@@ -35,7 +35,13 @@ import multiprocessing.managers
 import multiprocessing.heap
 import multiprocessing.pool
 
-from multiprocessing import util, reduction
+from multiprocessing import util
+
+try:
+    from multiprocessing import reduction
+    HAS_REDUCTION = True
+except ImportError:
+    HAS_REDUCTION = False
 
 try:
     from multiprocessing.sharedctypes import Value, copy
@@ -1582,6 +1588,7 @@ class _TestConnection(BaseTestCase):
         os.write(fd, data)
         os.close(fd)
 
+    @unittest.skipUnless(HAS_REDUCTION, "test needs multiprocessing.reduction")
     def test_fd_transfer(self):
         if self.TYPE != 'processes':
             self.skipTest("only makes sense with processes")
@@ -1600,6 +1607,7 @@ class _TestConnection(BaseTestCase):
         with open(test.support.TESTFN, "rb") as f:
             self.assertEqual(f.read(), b"foo")
 
+    @unittest.skipUnless(HAS_REDUCTION, "test needs multiprocessing.reduction")
     @unittest.skipIf(sys.platform == "win32",
                      "test semantics don't make sense on Windows")
     @unittest.skipIf(MAXFD <= 256,
@@ -1636,6 +1644,7 @@ class _TestConnection(BaseTestCase):
     def _send_data_without_fd(self, conn):
         os.write(conn.fileno(), b"\0")
 
+    @unittest.skipUnless(HAS_REDUCTION, "test needs multiprocessing.reduction")
     @unittest.skipIf(sys.platform == "win32", "doesn't make sense on Windows")
     def test_missing_fd_transfer(self):
         # Check that exception is raised when received data is not
@@ -1957,10 +1966,12 @@ class _TestImportStar(BaseTestCase):
             'multiprocessing', 'multiprocessing.connection',
             'multiprocessing.heap', 'multiprocessing.managers',
             'multiprocessing.pool', 'multiprocessing.process',
-            'multiprocessing.reduction',
             'multiprocessing.synchronize', 'multiprocessing.util'
             ]
 
+        if HAS_REDUCTION:
+            modules.append('multiprocessing.reduction')
+
         if c_int is not None:
             # This module requires _ctypes
             modules.append('multiprocessing.sharedctypes')