fully support isolation_level parameter in base dialect

Generalized the :paramref:`_sa.create_engine.isolation_level` parameter to
the base dialect so that it is no longer dependent on individual dialects
to be present. This parameter sets up the "isolation level" setting to
occur for all new database connections as soon as they are created by the
connection pool, where the value then stays set without being reset on
every checkin.

The :paramref:`_sa.create_engine.isolation_level` parameter is essentially
equivalent in functionality to using the
:paramref:`_engine.Engine.execution_options.isolation_level` parameter via
:meth:`_engine.Engine.execution_options` for an engine-wide setting. The
difference is in that the former setting assigns the isolation level just
once when a connection is created, the latter sets and resets the given
level on each connection checkout.

Fixes: #6342
Change-Id: Id81d6b1c1a94371d901ada728a610696e09e9741

1 files changed, 7 insertions, 3 deletions

diff --git a/lib/sqlalchemy/testing/assertions.py b/lib/sqlalchemy/testing/assertions.py
index c30fdf823..3aa2649f4 100644
--- a/lib/sqlalchemy/testing/assertions.py
+++ b/lib/sqlalchemy/testing/assertions.py
@@ -384,9 +384,13 @@ def _expect_raises(except_cls, msg=None, check_context=False):
         ec.error = err
         success = True
         if msg is not None:
-            assert re.search(
-                msg, util.text_type(err), re.UNICODE
-            ), "%r !~ %s" % (msg, err)
+            # I'm often pdbing here, and "err" above isn't
+            # in scope, so assign the string explicitly
+            error_as_string = util.text_type(err)
+            assert re.search(msg, error_as_string, re.UNICODE), "%r !~ %s" % (
+                msg,
+                error_as_string,
+            )
         if check_context and not are_we_already_in_a_traceback:
             _assert_proper_exception_context(err)
         print(util.text_type(err).encode("utf-8"))