Keep presets loading with bad local state (#1417)

tests/test_preset_local_storage_js.py

@@ -0,0 +1,53 @@
+import json
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+_REPO = Path(__file__).resolve().parent.parent
+_MODULE = _REPO / "static" / "js" / "presets.js"
+_HAS_NODE = shutil.which("node") is not None
+
+
+def _load_values():
+    js = f"""
+    globalThis.localStorage = {{
+      getItem(key) {{
+        return {{
+          broken: '{{',
+          list: '[]',
+          object: '{{"session":"Socrates"}}',
+        }}[key] ?? null;
+      }},
+    }};
+    const presets = await import('{_MODULE.as_posix()}');
+    console.log(JSON.stringify({{
+      brokenArray: presets.loadStoredArray('broken'),
+      wrongArray: presets.loadStoredArray('object'),
+      brokenObject: presets.loadStoredObject('broken'),
+      wrongObject: presets.loadStoredObject('list'),
+      object: presets.loadStoredObject('object'),
+    }}));
+    """
+    proc = subprocess.run(
+        ["node", "--input-type=module"],
+        input=js,
+        capture_output=True,
+        text=True,
+        cwd=str(_REPO),
+        timeout=30,
+    )
+    assert proc.returncode == 0, proc.stderr
+    return json.loads(proc.stdout.strip())
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_preset_storage_helpers_fall_back_for_bad_values():
+    assert _load_values() == {
+        "brokenArray": [],
+        "wrongArray": [],
+        "brokenObject": {},
+        "wrongObject": {},
+        "object": {"session": "Socrates"},
+    }