mock fetch test for fetch_voc function

tests/test_fetch_voc.py

@@ -5,12 +5,34 @@
 # invenio-subjects-CESSDA is free software, you can redistribute it and/or
 # modify it under the terms of the MIT License; see LICENSE file details.
 
+from unittest.mock import MagicMock, patch
+
+import pytest
+
 from invenio_subjects_cessda.fetch_voc import fetch_voc
 from tests.data import urls_to_fetch
 
+# Sample data to mock response from the API
+mock_response_data = [
+    {"name": "sample_voc1", "data": {"key": "value"}},
+    {"name": "sample_voc2", "data": {"key": "value"}},
+]
+
+
+@pytest.mark.asyncio
+async def test_fetch_voc():
+    """Test fetch_voc function."""
+
+    async def mock_json():
+        return {"key": "value"}
+
+    async def mock_get():
+        mock_resp = MagicMock()
+        mock_resp.json = mock_json
+        return mock_resp
 
-# @pytest.mark.asyncio
-def test_fetch_voc():
-    """Test fetch_voc."""
-    fetch_res = fetch_voc(urls_to_fetch)
-    assert len(fetch_res) == len(urls_to_fetch)
+    with patch("aiohttp.ClientSession.get", new=mock_get):
+        fetch_res = await fetch_voc(urls_to_fetch)
+        assert len(fetch_res) == len(urls_to_fetch)
+        for item in fetch_res:
+            assert item in mock_response_data