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, 36 insertions, 0 deletions

diff --git a/lib/sqlalchemy/testing/requirements.py b/lib/sqlalchemy/testing/requirements.py
index 5eb769bf3..5ee0d67a2 100644
--- a/lib/sqlalchemy/testing/requirements.py
+++ b/lib/sqlalchemy/testing/requirements.py
@@ -703,6 +703,42 @@ class SuiteRequirements(Requirements):
         return exclusions.closed()
 
     @property
+    def isolation_level(self):
+        """target dialect supports general isolation level settings.
+
+        Note that this requirement, when enabled, also requires that
+        the get_isolation_levels() method be implemented.
+
+        """
+        return exclusions.closed()
+
+    def get_isolation_levels(self, config):
+        """Return a structure of supported isolation levels for the current
+        testing dialect.
+
+        The structure indicates to the testing suite what the expected
+        "default" isolation should be, as well as the other values that
+        are accepted.  The dictionary has two keys, "default" and "supported".
+        The "supported" key refers to a list of all supported levels and
+        it should include AUTOCOMMIT if the dialect supports it.
+
+        If the :meth:`.DefaultRequirements.isolation_level` requirement is
+        not open, then this method has no return value.
+
+        E.g.::
+
+            >>> testing.requirements.get_isolation_levels()
+            {
+                "default": "READ_COMMITED",
+                "supported": [
+                    "SERIALIZABLE", "READ UNCOMMITTED",
+                    "READ COMMITTED", "REPEATABLE READ",
+                    "AUTOCOMMIT"
+                ]
+            }
+        """
+
+    @property
     def json_type(self):
         """target platform implements a native JSON type."""