diff --git a/tests/test_synthesizer.py b/tests/test_synthesizer.py
new file mode 100644
index 0000000..022add6
--- /dev/null
+++ b/tests/test_synthesizer.py
@@ -0,0 +1,80 @@
+import pytest
+from unittest.mock import AsyncMock
+from axon.models import SearchResult
+
+
+def make_results(n=3):
+    return [
+        SearchResult(title=f"T{i}", url=f"https://ex{i}.com", content=f"Content {i}", score=0.9)
+        for i in range(n)
+    ]
+
+
+@pytest.mark.asyncio
+async def test_synthesize_answer_returns_string(monkeypatch):
+    fake_response = {
+        "choices": [{"message": {"content": "The answer is 42."}}]
+    }
+
+    class FakeResponse:
+        def raise_for_status(self): pass
+        def json(self): return fake_response
+
+    class FakeClient:
+        async def __aenter__(self): return self
+        async def __aexit__(self, *_): pass
+        async def post(self, *args, **kwargs): return FakeResponse()
+
+    monkeypatch.setattr("axon.services.synthesizer.httpx.AsyncClient", FakeClient)
+
+    from axon.services.synthesizer import synthesize_answer
+    answer = await synthesize_answer("What is the answer?", make_results())
+    assert answer == "The answer is 42."
+
+
+@pytest.mark.asyncio
+async def test_synthesize_answer_empty_results():
+    from axon.services.synthesizer import synthesize_answer
+    answer = await synthesize_answer("query", [])
+    assert "No search results" in answer
+
+
+@pytest.mark.asyncio
+async def test_generate_sub_queries_parses_lines(monkeypatch):
+    fake_response = {
+        "choices": [{"message": {"content": "Query one\nQuery two\nQuery three"}}]
+    }
+
+    class FakeResponse:
+        def raise_for_status(self): pass
+        def json(self): return fake_response
+
+    class FakeClient:
+        async def __aenter__(self): return self
+        async def __aexit__(self, *_): pass
+        async def post(self, *args, **kwargs): return FakeResponse()
+
+    monkeypatch.setattr("axon.services.synthesizer.httpx.AsyncClient", FakeClient)
+
+    from axon.services.synthesizer import generate_sub_queries
+    queries = await generate_sub_queries("main topic", count=3)
+    assert len(queries) == 3
+    assert queries[0] == "Query one"
+
+
+@pytest.mark.asyncio
+async def test_generate_sub_queries_fallback_on_error(monkeypatch):
+    import httpx
+
+    class FakeClient:
+        async def __aenter__(self): return self
+        async def __aexit__(self, *_): pass
+        async def post(self, *args, **kwargs):
+            raise httpx.ConnectError("LLM down")
+
+    monkeypatch.setattr("axon.services.synthesizer.httpx.AsyncClient", FakeClient)
+
+    from axon.services.synthesizer import generate_sub_queries
+    queries = await generate_sub_queries("main topic", count=3)
+    assert len(queries) == 3
+    assert "main topic" in queries[0]