chore(backend): add duplicate route baseline regenerator

backend/tests/test_regen_duplicate_routes_baseline.py

@@ -0,0 +1,63 @@
+from __future__ import annotations
+
+import json
+from types import SimpleNamespace
+
+from scripts.regen_duplicate_routes_baseline import (
+    build_baseline_payload,
+    collect_duplicate_routes,
+    write_baseline,
+)
+
+
+def _route(path: str, methods: set[str], module: str):
+    def endpoint():
+        return None
+
+    endpoint.__module__ = module
+    return SimpleNamespace(path=path, methods=methods, endpoint=endpoint)
+
+
+def test_collect_duplicate_routes_matches_ci_guard_shape():
+    routes = [
+        _route("/api/layers", {"POST"}, "routers.data"),
+        _route("/api/layers", {"POST"}, "main"),
+        _route("/api/health", {"GET", "HEAD"}, "routers.health"),
+        _route("/api/health", {"GET", "HEAD"}, "main"),
+        _route("/api/only-once", {"GET"}, "routers.example"),
+        SimpleNamespace(path=None, methods={"GET"}, endpoint=lambda: None),
+    ]
+
+    assert collect_duplicate_routes(routes) == {
+        "GET /api/health": ["main", "routers.health"],
+        "POST /api/layers": ["main", "routers.data"],
+    }
+
+
+def test_build_baseline_payload_is_deterministic():
+    payload = build_baseline_payload(
+        {
+            "POST /z": ["routers.z", "main"],
+            "GET /a": ["routers.a", "main"],
+        }
+    )
+
+    assert list(payload["duplicates"]) == ["GET /a", "POST /z"]
+    assert payload["duplicates"]["GET /a"] == ["main", "routers.a"]
+    assert payload["_meta"]["issue"] == "#239"
+    assert payload["_meta"]["generated_with"] == (
+        "python -m scripts.regen_duplicate_routes_baseline"
+    )
+
+
+def test_write_baseline_emits_stable_json(tmp_path):
+    output = tmp_path / "duplicate_routes_baseline.json"
+    duplicates = {"POST /api/layers": ["routers.data", "main"]}
+
+    payload = write_baseline(output, duplicates=duplicates)
+
+    assert json.loads(output.read_text(encoding="utf-8")) == payload
+    assert output.read_text(encoding="utf-8").endswith("\n")
+    assert payload["duplicates"] == {
+        "POST /api/layers": ["main", "routers.data"]
+    }