diff --git a/backend/tests/test_plex_routes.py b/backend/tests/test_plex_routes.py
new file mode 100644
index 00000000..a6a51967
--- /dev/null
+++ b/backend/tests/test_plex_routes.py
@@ -0,0 +1,66 @@
+"""The Plex pages' local reads and the one local-only write, through HTTP.
+
+The service tests (`test_plex_service.py`) hold what each read and write does; these hold that the
+route calls it, commits — the `db` fixture fails a test whose handler left a write uncommitted —
+and what a client sees back. None of these reach Plex. Needs the DB.
+"""
+
+from app.plex.models import PlexCollection, PlexItem, PlexLibrary
+
+
+def _seed(db):
+    lib = PlexLibrary(plex_key="1", title="Movies", kind="movie", enabled=True)
+    db.add(lib)
+    db.flush()
+    db.add_all(
+        [
+            PlexItem(rating_key="m1", library_id=lib.id, kind="movie", title="M"),
+            PlexCollection(rating_key="c1", library_id=lib.id, title="Mine"),
+            PlexCollection(rating_key="c2", library_id=lib.id, title="IMDb Top 250"),
+        ]
+    )
+    db.commit()
+
+
+def test_an_admin_marks_a_collection_editable_and_it_stays(db, make_user, as_user):
+    _seed(db)
+    admin = as_user(make_user(role="admin"))
+    r = admin.post("/api/plex/collections/c1/editable", json={"editable": True})
+    assert r.status_code == 200, r.text
+    assert (r.json()["editable"], r.json()["can_edit"]) == (True, True)
+    db.expire_all()
+    listed = admin.get("/api/plex/collections").json()["collections"]
+    assert {c["id"]: c["editable"] for c in listed} == {"c1": True, "c2": False}
+    # An auto-list is never editable.
+    r = admin.post("/api/plex/collections/c2/editable", json={"editable": True})
+    assert r.status_code == 400
+    assert (
+        admin.post("/api/plex/collections/c9/editable", json={"editable": True}).status_code == 404
+    )
+
+
+def test_the_library_list_and_a_movie_page_read_from_the_mirror(
+    db, make_user, as_user, monkeypatch
+):
+    from app.routes.plex import detail
+
+    _seed(db)
+    client = as_user(make_user())
+    libs = client.get("/api/plex/libraries").json()["libraries"]
+    assert [(lib["key"], lib["count"]) for lib in libs] == [("1", 1)]
+
+    class _NoPlex:
+        def __init__(self, db):
+            from app.plex.client import PlexNotConfigured
+
+            raise PlexNotConfigured()
+
+    monkeypatch.setattr(detail, "PlexClient", _NoPlex)
+    body = client.get("/api/plex/item/m1").json()
+    assert (body["id"], body["library"], body["status"], body["collections"]) == (
+        "m1",
+        "1",
+        "new",
+        [],
+    )
+    assert client.get("/api/plex/item/nope").json()["detail"]["reason"] == "plex_item"