add a test to lock in index change order

tests/unit/test_materialized_view.py

@@ -0,0 +1,56 @@
+from copy import deepcopy
+
+from dbt.adapters.contracts.relation import RelationType
+from dbt.adapters.relation_configs.config_change import RelationConfigChangeAction
+
+from dbt.adapters.postgres.relation import PostgresRelation
+from dbt.adapters.postgres.relation_configs import PostgresIndexConfig
+
+
+def test_index_config_changes():
+    index_0_old = {
+        "column_names": {"column_0"},
+        "unique": True,
+        "method": "btree",
+    }
+    index_1_old = {
+        "column_names": {"column_1"},
+        "unique": True,
+        "method": "btree",
+    }
+    index_2_old = {
+        "column_names": {"column_2"},
+        "unique": True,
+        "method": "btree",
+    }
+    existing_indexes = frozenset(
+        PostgresIndexConfig.from_dict(index) for index in [index_0_old, index_1_old, index_2_old]
+    )
+
+    index_0_new = deepcopy(index_0_old)
+    index_2_new = deepcopy(index_2_old)
+    index_2_new.update(method="hash")
+    index_3_new = {
+        "column_names": {"column_3"},
+        "unique": True,
+        "method": "hash",
+    }
+    new_indexes = frozenset(
+        PostgresIndexConfig.from_dict(index) for index in [index_0_new, index_2_new, index_3_new]
+    )
+
+    relation = PostgresRelation.create(
+        database="my_database",
+        schema="my_schema",
+        identifier="my_materialized_view",
+        type=RelationType.MaterializedView,
+    )
+
+    index_changes = relation._get_index_config_changes(existing_indexes, new_indexes)
+
+    assert isinstance(index_changes, list)
+    assert len(index_changes) == len(["drop 1", "drop 2", "create 2", "create 3"])
+    assert index_changes[0].action == RelationConfigChangeAction.drop
+    assert index_changes[1].action == RelationConfigChangeAction.drop
+    assert index_changes[2].action == RelationConfigChangeAction.create
+    assert index_changes[3].action == RelationConfigChangeAction.create