Fix issue #1530.
Return an error exit status if not all tests passes.
diff --git a/Lib/doctest.py b/Lib/doctest.py
index 5ba2d2d..e8bd534 100644
--- a/Lib/doctest.py
+++ b/Lib/doctest.py
@@ -2657,12 +2657,15 @@
                 sys.path.insert(0, dirname)
                 m = __import__(filename[:-3])
                 del sys.path[0]
-                testmod(m)
+                failures, _ = testmod(m)
             else:
-                testfile(filename, module_relative=False)
+                failures, _ = testfile(filename, module_relative=False)
+            if failures:
+                return 1
     else:
         r = unittest.TextTestRunner()
         r.run(DocTestSuite())
+    return 0
 
 if __name__ == "__main__":
-    _test()
+    sys.exit(_test())