CVE-2020-25722 pytest: assertRaisesLdbError invents a message if you're lazy

This makes it easier to convert tests that don't have good messages.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14564

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

python/samba/tests/__init__.py

@@ -208,6 +208,8 @@ class TestCase(unittest.TestCase):
 
     def assertRaisesLdbError(self, errcode, message, f, *args, **kwargs):
         """Assert a function raises a particular LdbError."""
+        if message is None:
+            message = f"{f.__name__}(*{args}, **{kwargs})"
         try:
             f(*args, **kwargs)
         except ldb.LdbError as e: