Prepare rollback-safe legacy migration data contract (#7)

tests/unit/test_migration_maintenance.py

@@ -0,0 +1,45 @@
+from unittest.mock import Mock, patch
+
+import pytest
+from django.http import HttpResponse
+from django.test import RequestFactory
+
+from apps.core.middleware import MigrationMaintenanceMiddleware
+
+
+@pytest.mark.parametrize("method,path,allowed", [
+    ("GET", "/health/ready/", True),
+    ("HEAD", "/health/live/", True),
+    ("POST", "/health/ready/", False),
+    ("GET", "/health/ready", False),
+    ("GET", "/", False),
+    ("POST", "/accounts/login/", False),
+    ("OPTIONS", "/health/live/", False),
+])
+def test_held_candidate_only_allows_exact_safe_health(method, path, allowed):
+    downstream = Mock(return_value=HttpResponse("ok"))
+    with patch("apps.core.middleware.hold_active", return_value=True):
+        response = MigrationMaintenanceMiddleware(downstream)(
+            RequestFactory().generic(method, path)
+        )
+    assert response.status_code == (200 if allowed else 503)
+    assert downstream.called is allowed
+    if not allowed:
+        assert response["Cache-Control"] == "no-store"
+
+
+@pytest.mark.parametrize("failure", [PermissionError(), RuntimeError()])
+def test_marker_errors_block_ordinary_traffic(failure):
+    downstream = Mock()
+    with patch("apps.core.middleware.hold_active", side_effect=failure):
+        response = MigrationMaintenanceMiddleware(downstream)(RequestFactory().get("/"))
+    assert response.status_code == 503
+    downstream.assert_not_called()
+
+
+def test_normal_runtime_unchanged_and_middleware_is_first(settings):
+    assert settings.MIDDLEWARE[0] == "apps.core.middleware.MigrationMaintenanceMiddleware"
+    downstream = Mock(return_value=HttpResponse("ok"))
+    with patch("apps.core.middleware.hold_active", return_value=False):
+        response = MigrationMaintenanceMiddleware(downstream)(RequestFactory().post("/"))
+    assert response.status_code == 200