[recorder] Add tests for full schema migration (#5831)

* [recorder] Add tests for full schema migration

* Remove leftover code

* Fix duplicate creation of sqlalchemy Index object

* It's that kind of day...

* Improve models_original docstring

tests/components/recorder/test_init.py

@@ -6,15 +6,18 @@ import unittest
 from unittest.mock import patch, call, MagicMock
 
 import pytest
+from sqlalchemy import create_engine
+
 from homeassistant.core import callback
 from homeassistant.const import MATCH_ALL
 from homeassistant.components import recorder
 from homeassistant.bootstrap import setup_component
 from tests.common import get_test_home_assistant
+from tests.components.recorder import models_original
 
 
-class TestRecorder(unittest.TestCase):
-    """Test the recorder module."""
+class BaseTestRecorder(unittest.TestCase):
+    """Base class for common recorder tests."""
 
     def setUp(self):  # pylint: disable=invalid-name
         """Setup things to be run when tests are started."""
@@ -87,6 +90,10 @@ class TestRecorder(unittest.TestCase):
                     time_fired=timestamp,
                 ))
 
+
+class TestRecorder(BaseTestRecorder):
+    """Test the recorder module."""
+
     def test_saving_state(self):
         """Test saving and restoring a state."""
         entity_id = 'test.recorder'
@@ -205,15 +212,48 @@ class TestRecorder(unittest.TestCase):
         with self.assertRaises(ValueError):
             recorder._INSTANCE._apply_update(-1)
 
+
+def create_engine_test(*args, **kwargs):
+    """Test version of create_engine that initializes with old schema.
+
+    This simulates an existing db with the old schema.
+    """
+    engine = create_engine(*args, **kwargs)
+    models_original.Base.metadata.create_all(engine)
+    return engine
+
+
+class TestMigrateRecorder(BaseTestRecorder):
+    """Test recorder class that starts with an original schema db."""
+
+    @patch('sqlalchemy.create_engine', new=create_engine_test)
+    @patch('homeassistant.components.recorder.Recorder._migrate_schema')
+    def setUp(self, migrate):  # pylint: disable=invalid-name
+        """Setup things to be run when tests are started.
+
+        create_engine is patched to create a db that starts with the old
+        schema.
+
+        _migrate_schema is mocked to ensure it isn't run, so we can test it
+        below.
+        """
+        super().setUp()
+
     def test_schema_update_calls(self):  # pylint: disable=no-self-use
         """Test that schema migrations occurr in correct order."""
-        test_version = recorder.models.SchemaChanges(schema_version=0)
-        with recorder.session_scope() as session:
-            session.add(test_version)
-            with patch.object(recorder._INSTANCE, '_apply_update') as update:
-                recorder._INSTANCE._migrate_schema()
-                update.assert_has_calls([call(version+1) for version in range(
-                    0, recorder.models.SCHEMA_VERSION)])
+        with patch.object(recorder._INSTANCE, '_apply_update') as update:
+            recorder._INSTANCE._migrate_schema()
+            update.assert_has_calls([call(version+1) for version in range(
+                0, recorder.models.SCHEMA_VERSION)])
+
+    def test_schema_migrate(self):  # pylint: disable=no-self-use
+        """Test the full schema migration logic.
+
+        We're just testing that the logic can execute successfully here without
+        throwing exceptions. Maintaining a set of assertions based on schema
+        inspection could quickly become quite cumbersome.
+        """
+        recorder._INSTANCE._migrate_schema()
 
 
 @pytest.fixture