Issue #13854: Properly handle non-integer, non-string arg to SystemExit

Previously multiprocessing only expected int or str.  It also wrongly
used an exit code of 1 when the argument was a string instead of zero.

Lib/test/test_multiprocessing.py

@@ -325,6 +325,36 @@ class _TestProcess(BaseTestCase):
             ]
         self.assertEqual(result, expected)
 
+    @classmethod
+    def _test_sys_exit(cls, reason, testfn):
+        sys.stderr = open(testfn, 'w')
+        sys.exit(reason)
+
+    def test_sys_exit(self):
+        # See Issue 13854
+        if self.TYPE == 'threads':
+            return
+
+        testfn = test_support.TESTFN
+        self.addCleanup(test_support.unlink, testfn)
+
+        for reason, code in (([1, 2, 3], 1), ('ignore this', 0)):
+            p = self.Process(target=self._test_sys_exit, args=(reason, testfn))
+            p.daemon = True
+            p.start()
+            p.join(5)
+            self.assertEqual(p.exitcode, code)
+
+            with open(testfn, 'r') as f:
+                self.assertEqual(f.read().rstrip(), str(reason))
+
+        for reason in (True, False, 8):
+            p = self.Process(target=sys.exit, args=(reason,))
+            p.daemon = True
+            p.start()
+            p.join(5)
+            self.assertEqual(p.exitcode, reason)
+
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