Simplify choice()'s interaction with the private _randbelow() method (GH-19831)

diff --git a/Lib/test/test_random.py b/Lib/test/test_random.py
index 42c68dd..6d87d21 100644
--- a/Lib/test/test_random.py
+++ b/Lib/test/test_random.py
@@ -688,10 +688,10 @@
                 maxsize+1, maxsize=maxsize
             )
         self.gen._randbelow_without_getrandbits(5640, maxsize=maxsize)
-        # issue 33203: test that _randbelow raises ValueError on
+        # issue 33203: test that _randbelow returns zero on
         # n == 0 also in its getrandbits-independent branch.
-        with self.assertRaises(ValueError):
-            self.gen._randbelow_without_getrandbits(0, maxsize=maxsize)
+        x = self.gen._randbelow_without_getrandbits(0, maxsize=maxsize)
+        self.assertEqual(x, 0)
 
         # This might be going too far to test a single line, but because of our
         # noble aim of achieving 100% test coverage we need to write a case in