Initial commit: Sibilla — self-hosted Perplexity-like AI search engine

- Flask web app with Perplexity-style search + synthesis pipeline
- Degoog → SearXNG → DuckDuckGo cascading search backends
- Gemini LLM for query expansion + answer synthesis with citations
- MCP server exposing search tools via stdio
- 57 unit tests covering all modules

tests/test_ai.py

@@ -0,0 +1,135 @@
+"""Tests for sibilla.ai — GeminiClient with mocked API."""
+
+import pytest
+from unittest import mock
+from sibilla.ai import GeminiClient, SynthesisResult
+
+
+class TestSynthesisResult:
+    def test_defaults(self):
+        sr = SynthesisResult(answer="")
+        assert sr.answer == ""
+        assert sr.model == ""
+        assert sr.tokens_used == 0
+        assert sr.error is None
+
+
+class TestGeminiClient:
+    def test_no_api_key_returns_error(self):
+        client = GeminiClient(api_key="")
+        result = client.synthesize("system", "user")
+        assert result.answer == ""
+        assert "GOOGLE_API_KEY" in result.error
+
+    def test_lazy_client_raises_without_key(self):
+        client = GeminiClient(api_key="")
+        with pytest.raises(ValueError, match="GOOGLE_API_KEY"):
+            _ = client.client
+
+    def test_synthesize_success(self):
+        client = GeminiClient(api_key="fake-key")
+        mock_genai = mock.MagicMock()
+        client._client = mock_genai
+
+        mock_part = mock.MagicMock()
+        mock_part.text = "This is the answer."
+        mock_content = mock.MagicMock()
+        mock_content.parts = [mock_part]
+        mock_candidate = mock.MagicMock()
+        mock_candidate.content = mock_content
+        mock_usage = mock.MagicMock()
+        mock_usage.total_token_count = 42
+        mock_response = mock.MagicMock()
+        mock_response.candidates = [mock_candidate]
+        mock_response.usage_metadata = mock_usage
+
+        mock_genai.models.generate_content.return_value = mock_response
+
+        result = client.synthesize("system prompt", "user query")
+
+        assert result.answer == "This is the answer."
+        assert result.tokens_used == 42
+        assert result.model == "gemini-2.5-flash"
+        assert result.error is None
+
+    def test_synthesize_no_candidates(self):
+        client = GeminiClient(api_key="fake-key")
+        mock_genai = mock.MagicMock()
+        client._client = mock_genai
+
+        mock_response = mock.MagicMock()
+        mock_response.candidates = []
+        mock_response.usage_metadata = None
+        mock_genai.models.generate_content.return_value = mock_response
+
+        result = client.synthesize("s", "u")
+        assert result.answer == ""
+        assert result.error is None
+
+    def test_synthesize_api_exception(self):
+        client = GeminiClient(api_key="fake-key")
+        mock_genai = mock.MagicMock()
+        client._client = mock_genai
+
+        mock_genai.models.generate_content.side_effect = RuntimeError("API down")
+
+        result = client.synthesize("s", "u")
+        assert result.error == "API down"
+        assert result.answer == ""
+
+    def test_rewrite_query_no_api_key(self):
+        client = GeminiClient(api_key="")
+        variants = client.rewrite_query("test query", num_variants=3)
+        assert variants == ["test query"]
+
+    def test_rewrite_query_success(self):
+        client = GeminiClient(api_key="fake-key")
+        mock_genai = mock.MagicMock()
+        client._client = mock_genai
+
+        mock_part = mock.MagicMock()
+        mock_part.text = "rewritten query 1\nrewritten query 2\nrewritten query 3"
+        mock_content = mock.MagicMock()
+        mock_content.parts = [mock_part]
+        mock_candidate = mock.MagicMock()
+        mock_candidate.content = mock_content
+        mock_response = mock.MagicMock()
+        mock_response.candidates = [mock_candidate]
+        mock_genai.models.generate_content.return_value = mock_response
+
+        variants = client.rewrite_query("original", num_variants=3)
+
+        assert len(variants) == 4
+        assert variants[0] == "original"
+        assert "rewritten query 1" in variants
+
+    def test_rewrite_query_strips_bullets(self):
+        client = GeminiClient(api_key="fake-key")
+        mock_genai = mock.MagicMock()
+        client._client = mock_genai
+
+        mock_part = mock.MagicMock()
+        mock_part.text = "- bullet query\n• dot query"
+        mock_content = mock.MagicMock()
+        mock_content.parts = [mock_part]
+        mock_candidate = mock.MagicMock()
+        mock_candidate.content = mock_content
+        mock_response = mock.MagicMock()
+        mock_response.candidates = [mock_candidate]
+        mock_genai.models.generate_content.return_value = mock_response
+
+        variants = client.rewrite_query("original", num_variants=2)
+
+        assert "bullet query" in variants
+        assert "dot query" in variants
+        assert not any(v.startswith("-") for v in variants)
+
+    def test_rewrite_query_exception_fallback(self):
+        client = GeminiClient(api_key="fake-key")
+        mock_genai = mock.MagicMock()
+        client._client = mock_genai
+
+        mock_genai.models.generate_content.side_effect = RuntimeError("boom")
+
+        variants = client.rewrite_query("original", num_variants=2)
+        assert variants == ["original"]