test: consolidate suites and remove redundant cases (#1459)

Regression tests were scattered across feature- and bug-specific files, and some suites repeated the same checks. Group tests by responsibility, isolate feature fixtures in test classes, and remove duplicate or obsolete cases.

The review covered all 127 collected test modules on main. This reduces them and removes or combines definitions:.

 No application code changes.

tests/test_configmigrate.py

@@ -1,6 +1,7 @@
+# Test data directory and known migration pairs
+import copy
 import json
 import shutil
-import tempfile
 from pathlib import Path
 from typing import Any
 
@@ -8,9 +9,9 @@ import pytest
 
 from akkudoktoreos.config import configmigrate
 from akkudoktoreos.config.config import ConfigEOS, SettingsEOSDefaults
+from akkudoktoreos.config.configmigrate import migrate_config_data
 from akkudoktoreos.core.version import __version__
 
-# Test data directory and known migration pairs
 DIR_TESTDATA = Path(__file__).absolute().parent.joinpath("testdata")
 
 MIGRATION_PAIRS = [
@@ -250,3 +251,16 @@ class TestConfigMigration:
             # Remove the .new working file only if the test passed (failed == False)
             if not failed and working_file.exists():
                 working_file.unlink(missing_ok=True)
+
+
+class TestDeviceMigration:
+    @pytest.mark.parametrize("as_list", [False, True])
+    def test_migration_preserves_lcos_and_input(self, as_list):
+        battery = {"device_id": "house", "capacity_wh": 12000,
+                   "levelized_cost_of_storage_kwh": 0.123}
+        raw = {"devices": {"batteries": [battery] if as_list else {"house": battery}}}
+        original = copy.deepcopy(raw)
+        migrated = migrate_config_data(raw)
+        assert migrated.devices.batteries is not None
+        assert migrated.devices.batteries["house"].levelized_cost_of_storage_amt_kwh == 0.123
+        assert raw == original