diff --git a/planty/application/tests/test_endpoints.py b/planty/application/tests/test_endpoints.py
index 2bff916..576eb8d 100644
--- a/planty/application/tests/test_endpoints.py
+++ b/planty/application/tests/test_endpoints.py
@@ -118,6 +118,7 @@ async def test_get_archived_tasks(
     "parent_id, status_code, error_detail",
     [
         ("0d966845-254b-4b5c-b8a7-8d34dcd3d527", 201, None),
+        ("45561eb6-3570-44de-af8a-54212e2981e6", 201, None),
         (
             "090eda97-dd2d-45bb-baa0-7814313e5a38",
             422,
@@ -132,18 +133,21 @@ async def test_create_section(
     ac: AsyncClient,
     additional_test_data: dict[str, Any],
 ) -> None:
-    section_data = {
-        "title": str(additional_test_data["sections"][0]["title"]),
-        "parent_id": parent_id,
-    }
-    response = await ac.post("/api/section", json=section_data)
-    assert response.status_code == status_code
-    if not response.is_success:
-        assert response.json()["detail"] == error_detail
-        return
+    # Do it twice to check that the `has_subsections` flag is updated correctly
+    # (there is no other way to check it using endpoints)
+    for _ in range(2):
+        section_data = {
+            "title": str(additional_test_data["sections"][0]["title"]),
+            "parent_id": parent_id,
+        }
+        response = await ac.post("/api/section", json=section_data)
+        assert response.status_code == status_code
+        if not response.is_success:
+            assert response.json()["detail"] == error_detail
+            return
 
-    data = response.json()
-    assert "id" in data
+        data = response.json()
+        assert "id" in data
 
 
 @pytest.mark.parametrize(
diff --git a/planty/conftest.py b/planty/conftest.py
index 8308756..d381183 100644
--- a/planty/conftest.py
+++ b/planty/conftest.py
@@ -40,6 +40,7 @@ def additional_test_data() -> dict[str, Any]:
 def _load_json_with_data(filename: str) -> dict[str, Any]:
     with open(Path(__file__).parent / "resources" / filename) as f:
         test_data: dict[str, Any] = json.load(f)
+    ids = set()
     for table_key in test_data:
         last_idx: int = 0
         for row in test_data[table_key]:
@@ -58,6 +59,10 @@ def _load_json_with_data(filename: str) -> dict[str, Any]:
                         "(NOTE: this is just a heuristic)"
                     )
                     last_idx = idx
+                if column == "id":
+                    if row[column] in ids:
+                        raise ValueError(f"Duplicate id {row[column]} in {table_key}")
+                    ids.add(row[column])
 
     # TODO: make this dict immutable to prevent accidental modification
     return test_data
diff --git a/planty/resources/data.json b/planty/resources/data.json
index 445059b..46f82f3 100644
--- a/planty/resources/data.json
+++ b/planty/resources/data.json
@@ -141,7 +141,7 @@
       "index": 2
     },
     {
-      "id": "f05b7527-8173-4d14-a1bd-49aaba743247",
+      "id": "45561eb6-3570-44de-af8a-54212e2981e6",
       "title": "🎸  Music",
       "user_id": "38df4136-36b2-4171-8459-27f411af8323",
       "parent_id": "36ea0a4f-0334-464d-8066-aa359ecfdcba",