diff --git a/tests/test_kani.py b/tests/test_kani.py
index 0a968f7..99bd741 100644
--- a/tests/test_kani.py
+++ b/tests/test_kani.py
@@ -1,5 +1,4 @@
-import random
-import string
+from hypothesis import HealthCheck, given, settings, strategies as st
 
 from kani import ChatMessage, ChatRole, Kani
 from tests.engine import TestEngine
@@ -45,13 +44,19 @@ async def test_always_include():
     assert flatten_chatmessages(prompt) == "12a"
 
 
-async def test_spam():
+@settings(suppress_health_check=(HealthCheck.too_slow,), deadline=None)
+@given(st.data())
+async def test_spam(data):
     # spam the kani with a bunch of random prompts
     # and make sure it never breaks
-    ai = Kani(engine, desired_response_tokens=3, system_prompt="1", always_included_messages=[ChatMessage.user("2")])
-    for _ in range(1000):
-        query_len = random.randint(0, 5)
-        query = "".join(random.choice(string.ascii_letters) for _ in range(query_len))
+    ai = Kani(
+        engine,
+        desired_response_tokens=3,
+        system_prompt=data.draw(st.text(min_size=0, max_size=1)),
+        always_included_messages=[ChatMessage.user(data.draw(st.text(min_size=0, max_size=1)))],
+    )
+    queries = data.draw(st.lists(st.text(min_size=0, max_size=5)))
+    for query in queries:
         resp = await ai.chat_round_str(query, test_echo=True)
         assert resp == query
 
diff --git a/tests/test_mock_openai.py b/tests/test_mock_openai.py
new file mode 100644
index 0000000..4b10760
--- /dev/null
+++ b/tests/test_mock_openai.py
@@ -0,0 +1,66 @@
+"""Ensure that any messages sent to OpenAI are valid (mock the API and just echo)."""
+
+import time
+
+from hypothesis import HealthCheck, given, settings, strategies as st
+from pydantic import RootModel
+
+from kani import ChatMessage, Kani
+from kani.engines.openai import OpenAIClient, OpenAIEngine
+from kani.engines.openai.models import OpenAIChatMessage
+
+
+class MockOpenAIClient(OpenAIClient):
+    async def request(self, method: str, route: str, headers=None, retry=None, **kwargs):
+        if route != "/chat/completions":
+            raise ValueError("only chat completions is mocked in tests")
+
+        # validate that all the messages come across correctly
+        data = kwargs["json"]
+        RootModel[list[OpenAIChatMessage]].model_validate(data["messages"])
+
+    async def post(self, route: str, **kwargs):
+        if route != "/chat/completions":
+            raise ValueError("only chat completions is mocked in tests")
+
+        await self.request("POST", route, **kwargs)
+        data = kwargs["json"]
+        message = data["messages"][-1] if data["messages"] else {"role": "assistant", "content": None}
+        return dict(
+            id="some-id",
+            object="chat.completion",
+            created=int(time.time()),
+            model=data["model"],
+            usage=dict(prompt_tokens=0, completion_tokens=0, total_tokens=0),
+            choices=[dict(message=message, index=0)],
+        )
+
+
+class MockOpenAIEngine(OpenAIEngine):
+    @staticmethod
+    def translate_messages(messages, cls=OpenAIChatMessage):
+        # we don't care about the tool call bindings here - just the translation
+        return [cls.from_chatmessage(m) for m in messages]
+
+
+client = MockOpenAIClient("sk-fake-api-key")
+engine = MockOpenAIEngine(client=client)
+
+
+# hypothesis synchronously constructs a coro to call MockOpenAIClient.create_chat_completion
+# based on the type annotations of the async function
+# we then await the returned coro in the async test body
+@settings(suppress_health_check=(HealthCheck.too_slow,), deadline=None)
+@given(st.builds(client.create_chat_completion))
+async def test_chat_completions_valid(coro):
+    await coro
+
+
+def build_kani_state(msgs: list[ChatMessage]):
+    return Kani(engine, chat_history=msgs)
+
+
+@settings(suppress_health_check=(HealthCheck.too_slow,), deadline=None)
+@given(st.builds(build_kani_state))
+async def test_kani_chatmessages_valid(ai):
+    await ai.get_model_completion()