Implement autocommit isolation level for cx_oracle

As part of this change Oracle also gets the concept of a
default isolation level, however since Oracle does not provide a
fixed method of knowing what the isolation level would be without a
server side transaction actually in progress, for now we hardcode
just to "READ COMMITTED".

Enhanced the test suite for isolation level testing in the dialect
test suite and added features to requirements so that the supported
isolation levels can be reported generically for dialects.

Co-authored-by: Mike Bayer <mike_mp@zzzcomputing.com>
Fixes: #5200
Change-Id: I2c4d49da9ff80ccc228c21e196ec9a961de53478

1 files changed, 10 insertions, 19 deletions

diff --git a/test/engine/test_transaction.py b/test/engine/test_transaction.py
index c6a6c5e3a..13058fbe1 100644
--- a/test/engine/test_transaction.py
+++ b/test/engine/test_transaction.py
@@ -882,28 +882,19 @@ class IsolationLevelTest(fixtures.TestBase):
     __backend__ = True
 
     def _default_isolation_level(self):
-        if testing.against("sqlite"):
-            return "SERIALIZABLE"
-        elif testing.against("postgresql"):
-            return "READ COMMITTED"
-        elif testing.against("mysql"):
-            return "REPEATABLE READ"
-        elif testing.against("mssql"):
-            return "READ COMMITTED"
-        else:
-            assert False, "default isolation level not known"
+        return testing.requires.get_isolation_levels(testing.config)["default"]
 
     def _non_default_isolation_level(self):
-        if testing.against("sqlite"):
-            return "READ UNCOMMITTED"
-        elif testing.against("postgresql"):
-            return "SERIALIZABLE"
-        elif testing.against("mysql"):
-            return "SERIALIZABLE"
-        elif testing.against("mssql"):
-            return "SERIALIZABLE"
+        levels = testing.requires.get_isolation_levels(testing.config)
+
+        default = levels["default"]
+        supported = levels["supported"]
+
+        s = set(supported).difference(["AUTOCOMMIT", default])
+        if s:
+            return s.pop()
         else:
-            assert False, "non default isolation level not known"
+            assert False, "no non-default isolation level available"
 
     def test_engine_param_stays(self):