Warn on non-Connection present and accommodate for Engine

A warning is emitted when an object that's not a
:class:`~sqlalchemy.engine.Connection` is passed to
:meth:`.EnvironmentContext.configure`.  For the case of a
:class:`~sqlalchemy.engine.Engine` passed, the check for "in transaction"
introduced in version 0.9.0 has been relaxed to work in the case of an
attribute error, as some users appear to be passing an
:class:`~sqlalchemy.engine.Engine` and not a
:class:`~sqlalchemy.engine.Connection`.

Change-Id: I95ef38955c00511d3055362a03284fb91677595f
Fixes: #419

1 files changed, 46 insertions, 2 deletions

diff --git a/tests/test_environment.py b/tests/test_environment.py
index cb8a0a2..42ff328 100644
--- a/tests/test_environment.py
+++ b/tests/test_environment.py
@@ -4,9 +4,10 @@ from alembic.script import ScriptDirectory
 from alembic.environment import EnvironmentContext
 from alembic.migration import MigrationContext
 from alembic.testing.fixtures import TestBase
-from alembic.testing.mock import Mock, call
+from alembic.testing.mock import Mock, call, MagicMock
 from alembic.testing.env import _no_sql_testing_config, \
-    staging_env, clear_staging_env
+    staging_env, clear_staging_env, write_script, _sqlite_file_db
+from alembic.testing.assertions import expect_warnings
 
 from alembic.testing import eq_, is_
 
@@ -74,3 +75,46 @@ class EnvironmentTest(TestBase):
 
         ctx = MigrationContext(ctx.dialect, None, {})
         is_(ctx.config, None)
+
+    def test_warning_on_passing_engine(self):
+        env = self._fixture()
+
+        engine = _sqlite_file_db()
+
+        a_rev = 'arev'
+        env.script.generate_revision(a_rev, "revision a", refresh=True)
+        write_script(env.script, a_rev, """\
+"Rev A"
+revision = '%s'
+down_revision = None
+
+from alembic import op
+
+
+def upgrade():
+    pass
+
+
+def downgrade():
+    pass
+
+""" % a_rev)
+        migration_fn = MagicMock()
+
+        def upgrade(rev, context):
+            migration_fn(rev, context)
+            return env.script._upgrade_revs(a_rev, rev)
+
+        with expect_warnings(
+                r"'connection' argument to configure\(\) is "
+                r"expected to be a sqlalchemy.engine.Connection "):
+            env.configure(
+                connection=engine, fn=upgrade,
+                transactional_ddl=False)
+
+        env.run_migrations()
+
+        eq_(
+            migration_fn.mock_calls,
+            [call((), env._migration_context)]
+        )