diff --git a/tests/test_cache.py b/tests/test_cache.py
new file mode 100644
index 0000000..1e0a19e
--- /dev/null
+++ b/tests/test_cache.py
@@ -0,0 +1,57 @@
+import asyncio
+import pytest
+
+
+@pytest.mark.asyncio
+async def test_inmemory_cache_miss():
+    from axon.services.cache import InMemoryCache
+    cache = InMemoryCache()
+    assert await cache.get("missing") is None
+
+
+@pytest.mark.asyncio
+async def test_inmemory_cache_set_and_get():
+    from axon.services.cache import InMemoryCache
+    cache = InMemoryCache()
+    await cache.set("k", "v", ttl=60)
+    assert await cache.get("k") == "v"
+
+
+@pytest.mark.asyncio
+async def test_inmemory_cache_expiry():
+    from axon.services.cache import InMemoryCache
+    cache = InMemoryCache()
+    await cache.set("k", "v", ttl=0)
+    # Force expiry by backdating
+    key = list(cache._store.keys())[0]
+    value, expires_at = cache._store[key]
+    from datetime import UTC, datetime, timedelta
+    cache._store[key] = (value, datetime.now(UTC) - timedelta(seconds=1))
+    assert await cache.get("k") is None
+
+
+@pytest.mark.asyncio
+async def test_inmemory_cache_ping():
+    from axon.services.cache import InMemoryCache
+    cache = InMemoryCache()
+    assert await cache.ping() is True
+
+
+def test_make_cache_key_is_deterministic():
+    from axon.services.cache import make_cache_key
+    k1 = make_cache_key("search", query="hello", max_results=10)
+    k2 = make_cache_key("search", query="hello", max_results=10)
+    assert k1 == k2
+
+
+def test_make_cache_key_differs_by_params():
+    from axon.services.cache import make_cache_key
+    k1 = make_cache_key("search", query="hello")
+    k2 = make_cache_key("search", query="world")
+    assert k1 != k2
+
+
+def test_make_cache_key_has_prefix():
+    from axon.services.cache import make_cache_key
+    k = make_cache_key("extract", url="https://x.com")
+    assert k.startswith("extract:")