✅(backend) test reranking function

I am adding test about reranking

src/backend/core/tests/test_reranking.py

@@ -0,0 +1,99 @@
+"""
+Test suite for reranking service
+"""
+
+import logging
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from core.services.reranking import rerank
+
+pytestmark = pytest.mark.django_db
+
+logger = logging.getLogger(__name__)
+
+
+ORIGINAL_HITS = [
+    {
+        "_id": "doc-0",
+        "_score": 1.5,
+        "_source": {
+            "title.en": "Dogs",
+            "content.en": "Dogs are domesticated wolves",
+        },
+    },
+    {
+        "_id": "doc-1",
+        "_score": 1.2,
+        "_source": {
+            "title.en": "Cats",
+            "content.en": "Cats are popular pets",
+        },
+    },
+    {
+        "_id": "doc-2",
+        "_score": 1.0,
+        "_source": {
+            "title.en": "Birds",
+            "content.en": "Birds fly in the sky",
+        },
+    },
+]
+
+
+@patch("core.services.reranking.get_reranker")
+def test_return_original_results_if_reranker_import_fails(mocked_get_reranker, caplog):
+    """Test that original results are returned if reranker import fails"""
+    mocked_get_reranker.return_value = None
+
+    with caplog.at_level(logging.WARNING):
+        result = rerank("test query", ORIGINAL_HITS)
+
+    assert result == ORIGINAL_HITS
+    assert any(
+        "Could not import reranker, returning original results" in message
+        for message in caplog.messages
+    )
+
+
+@patch("core.services.reranking.get_reranker")
+def test_return_original_results_if_reranking_fails(mocked_get_reranker, caplog):
+    """Test that original results are returned if reranking fails"""
+    mock_reranker = MagicMock()
+    mock_reranker.rerank.side_effect = Exception("Reranking service error")
+    mocked_get_reranker.return_value = mock_reranker
+
+    q = "test query"
+    with caplog.at_level(logging.ERROR):
+        result = rerank(q, ORIGINAL_HITS)
+
+    assert result == ORIGINAL_HITS
+    assert any(
+        "Reranking failed: Reranking service error, returning original results"
+        in message
+        for message in caplog.messages
+    )
+
+
+def test_reranking_success(caplog, settings):
+    """Test successful reranking of search results"""
+    settings.RERANKER_MODEL_NAME = "ms-marco-MiniLM-L-12-v2"
+
+    q = "cats"
+    with caplog.at_level(logging.INFO):
+        reranked_hits = rerank(q, ORIGINAL_HITS.copy())
+
+    assert any(
+        f"Reranking 3 results for query: {q}" in message for message in caplog.messages
+    )
+    assert any(
+        "Reranking completed, returned 3 results" in message
+        for message in caplog.messages
+    )
+
+    # if the reranking is not too bad it should definitely rerank doc-1 at top position
+    assert reranked_hits[0]["_id"] == ORIGINAL_HITS[1]["_id"]
+    # reranked_hits should be sorted by _reranked_score
+    assert reranked_hits[0]["_reranked_score"] > reranked_hits[1]["_reranked_score"]
+    assert reranked_hits[1]["_reranked_score"] > reranked_hits[2]["_reranked_score"]

src/backend/core/tests/test_search.py

@@ -5,6 +5,7 @@ Test suite for opensearch search service
 import logging
 import operator
 from json import dumps as json_dumps
+from unittest.mock import patch
 
 import pytest
 import responses
@@ -712,3 +713,41 @@ def test_search_filtering_by_query_path_and_tag():
 
     assert result["hits"]["total"]["value"] == len(documents_to_search)
     assert returned_ids == expected_ids
+
+
+@patch("core.services.search.rerank")
+def test_reranker_disabled(mocked_rerank, settings):
+    """Test that reranker is not called when disabled"""
+    settings.RERANKER_ENABLED = False
+    documents = bulk_create_documents(
+        [
+            {"title": "wolf", "content": "wolves live in packs and hunt together"},
+            {"title": "dog", "content": "dogs are loyal domestic animals"},
+            {"title": "cat", "content": "cats are curious and independent pets"},
+        ]
+    )
+    service = factories.ServiceFactory(name=SERVICE_NAME)
+    prepare_index(service.index_name, documents)
+
+    search(q="canine pet", **search_params(service))
+
+    mocked_rerank.assert_not_called()
+
+
+@patch("core.services.search.rerank")
+def test_reranker_enabled(mocked_rerank, settings):
+    """Test that reranker is called when enabled"""
+    settings.RERANKER_ENABLED = True
+    documents = bulk_create_documents(
+        [
+            {"title": "wolf", "content": "wolves live in packs and hunt together"},
+            {"title": "dog", "content": "dogs are loyal domestic animals"},
+            {"title": "cat", "content": "cats are curious and independent pets"},
+        ]
+    )
+    service = factories.ServiceFactory(name=SERVICE_NAME)
+    prepare_index(service.index_name, documents)
+
+    search(q="canine pet", **search_params(service))
+
+    mocked_rerank.assert_called_once()