test_hashlib: better handle support for SHA3

It's possible that the SSL library supports only SHA3 algo and doesn't
have SHAKE one.

The current test wrongly detect this and set both HASH and HASHXOF to
None expecting to have the extra SHA3 attributes present but this should
only be true for SHAKE algo.

To better handle this, move the HASH condition to a dedicated try-expect
condition and check if HASHXOF is None in the relevant code effectively
checking if SHA3 is supported by the SSL library but SHAKE algo needs to
use the sha3module one.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

Author: Ansuel

Lib/test/test_hashlib.py

@@ -40,9 +40,13 @@
 openssl_hashlib = import_fresh_module('hashlib', fresh=['_hashlib'])
 
 try:
-    from _hashlib import HASH, HASHXOF, openssl_md_meth_names, get_fips_mode
+    from _hashlib import HASH
 except ImportError:
     HASH = None
+
+try:
+    from _hashlib import HASHXOF, openssl_md_meth_names, get_fips_mode
+except ImportError:
     HASHXOF = None
     openssl_md_meth_names = frozenset()
 
@@ -631,9 +635,14 @@ def check_sha3(self, name, capacity, rate, suffix):
         constructors = self.constructors_to_test[name]
         for hash_object_constructor in constructors:
             m = hash_object_constructor()
-            if HASH is not None and isinstance(m, HASH):
-                # _hashopenssl's variant does not have extra SHA3 attributes
-                continue
+            if name.startswith('shake_'):
+                if HASHXOF is not None and isinstance(m, HASHXOF):
+                    # _hashopenssl's variant does not have extra SHA3 attributes
+                    continue
+            else:
+                if HASH is not None and isinstance(m, HASH):
+                    # _hashopenssl's variant does not have extra SHA3 attributes
+                    continue
             self.assertEqual(capacity + rate, 1600)
             self.assertEqual(m._capacity_bits, capacity)
             self.assertEqual(m._rate_bits, rate)
@@ -1156,7 +1165,8 @@ def test_disallow_instantiation(self):
     def test_hash_disallow_instantiation(self):
         # internal types like _hashlib.HASH are not constructable
         support.check_disallow_instantiation(self, HASH)
-        support.check_disallow_instantiation(self, HASHXOF)
+        if HASHXOF is not None:
+            support.check_disallow_instantiation(self, HASHXOF)
 
     def test_readonly_types(self):
         for algorithm, constructors in self.constructors_to_test.items():