Stricter versioning: always store migrate version record, file must be within versions included in migrations. Log only for migrations that made changes. Allow deleting older migration functions when no longer required.

tests/test_migrations.py

@@ -1,5 +1,9 @@
+import logging
 from types import ModuleType, SimpleNamespace
 
+import pytest
+
+from kanta.exceptions import DatabaseError
 from kanta.migrations import Migrations
 
 
@@ -89,3 +93,112 @@ def test_migration_can_omit_kanta_argument():
     new_ver = reg.apply(state, current_version=0, kanta=kanta, silent=True)
     assert new_ver == 1
     assert state["x"] == 1
+
+
+def test_version_too_new():
+    reg = Migrations()
+    kanta = _DummyKanta()
+
+    @reg.register
+    def migrate_v1(d):
+        d["x"] = 1
+
+    with pytest.raises(
+        DatabaseError,
+        match="Database version v2 is newer than the highest supported version v1",
+    ):
+        reg.apply({}, current_version=2, kanta=kanta, silent=True)
+
+
+def test_version_too_old():
+    reg = Migrations()
+    kanta = _DummyKanta()
+
+    @reg.register
+    def migrate_v3(d):
+        d["x"] = 3
+
+    with pytest.raises(
+        DatabaseError,
+        match="Database version v1 is older than the minimum supported version v2",
+    ):
+        reg.apply({}, current_version=1, kanta=kanta, silent=True)
+
+
+def test_missing_middle_migration_is_skipped():
+    reg = Migrations()
+    kanta = _DummyKanta()
+
+    @reg.register
+    def migrate_v1(d):
+        d["x"] = 1
+
+    @reg.register
+    def migrate_v3(d):
+        d["y"] = 3
+
+    state = {"x": 1}
+    new_ver = reg.apply(state, current_version=1, kanta=kanta, silent=True)
+    assert new_ver == 3
+    assert state["x"] == 1
+    assert state["y"] == 3
+
+
+def test_old_migrations_deleted_current_supported():
+    reg = Migrations()
+    kanta = _DummyKanta()
+
+    @reg.register
+    def migrate_v3(d):
+        d["x"] = 3
+
+    state = {"x": 2}
+    new_ver = reg.apply(state, current_version=2, kanta=kanta, silent=True)
+    assert new_ver == 3
+    assert state["x"] == 3
+
+
+def test_migration_log_only_when_changed(caplog):
+    reg = Migrations()
+    kanta = _DummyKanta()
+
+    @reg.register
+    def migrate_v1(d):
+        """Set x."""
+        d["x"] = 1
+
+    @reg.register
+    def migrate_v2(d):
+        """No-op."""
+        pass
+
+    @reg.register
+    def migrate_v3(d):
+        """Set y."""
+        d["y"] = 3
+
+    with caplog.at_level(logging.INFO, logger="kanta.migrations"):
+        reg.apply({}, current_version=0, kanta=kanta)
+
+    messages = [r.message for r in caplog.records if r.levelno == logging.INFO]
+    assert len(messages) == 2
+    assert "migrate_v1" in messages[0]
+    assert "Set x" in messages[0]
+    assert "migrate_v3" in messages[1]
+    assert "Set y" in messages[1]
+
+
+def test_no_op_migration_produces_no_log(caplog):
+    reg = Migrations()
+    kanta = _DummyKanta()
+
+    @reg.register
+    def migrate_v1(d):
+        """No-op."""
+        pass
+
+    with caplog.at_level(logging.INFO, logger="kanta.migrations"):
+        reg.apply({}, current_version=0, kanta=kanta)
+
+    info_messages = [r for r in caplog.records if r.levelno == logging.INFO]
+    assert not info_messages