resolve for variant before testing for schema type

Fixed regression where usage of a ``with_variant()`` datatype in
conjunction with the ``existing_type`` option of ``op.alter_column()``
under batch mode would lead to an internal exception.

note this exception would only occur under 1.x, under 2.0
the new variant architecture would have prevented this problem,
however it is best here that the ultimate variant type is
unwrapped in the case that we have a plain type with a
schema type as a variant.

also sqla 1.3 needs pytest < 7 to run correctly

Change-Id: I0f5480f97f014e707b8bd4e70f8495d3bd27fd21
Fixes: #982

1 files changed, 24 insertions, 0 deletions

diff --git a/tests/test_batch.py b/tests/test_batch.py
index 700056a..f0bbd75 100644
--- a/tests/test_batch.py
+++ b/tests/test_batch.py
@@ -1138,6 +1138,30 @@ class CopyFromTest(TestBase):
             "ALTER TABLE _alembic_tmp_foo RENAME TO foo",
         )
 
+    def test_change_name_from_existing_variant_type(self):
+        """test #982"""
+        context = self._fixture()
+        self.table.append_column(
+            Column("y", Text().with_variant(Text(10000), "mysql"))
+        )
+
+        with self.op.batch_alter_table(
+            "foo", copy_from=self.table
+        ) as batch_op:
+            batch_op.alter_column(
+                column_name="y",
+                new_column_name="q",
+                existing_type=Text().with_variant(Text(10000), "mysql"),
+            )
+        context.assert_(
+            "CREATE TABLE _alembic_tmp_foo (id INTEGER NOT NULL, "
+            "data VARCHAR(50), x INTEGER, q TEXT, PRIMARY KEY (id))",
+            "INSERT INTO _alembic_tmp_foo (id, data, x, q) "
+            "SELECT foo.id, foo.data, foo.x, foo.y FROM foo",
+            "DROP TABLE foo",
+            "ALTER TABLE _alembic_tmp_foo RENAME TO foo",
+        )
+
     def test_change_type_to_schematype(self):
         context = self._fixture()
         self.table.append_column(Column("y", Integer))