#13899: \A, \Z, and \B now correctly match the A, Z, and B literals when used inside character classes (e.g. [A]).  Patch by Matthew Barnett.
diff --git a/Lib/test/test_re.py b/Lib/test/test_re.py
index 70702e6..dee5efe 100644
--- a/Lib/test/test_re.py
+++ b/Lib/test/test_re.py
@@ -821,6 +821,12 @@
         # Test behaviour when not given a string or pattern as parameter
         self.assertRaises(TypeError, re.compile, 0)
 
+    def test_bug_13899(self):
+        # Issue #13899: re pattern r"[\A]" should work like "A" but matches
+        # nothing. Ditto B and Z.
+        self.assertEqual(re.findall(r'[\A\B\b\C\Z]', 'AB\bCZ'),
+                         ['A', 'B', '\b', 'C', 'Z'])
+
     @precisionbigmemtest(size=_2G, memuse=1)
     def test_large_search(self, size):
         # Issue #10182: indices were 32-bit-truncated.