diff --git a/tests/conftest.py b/tests/conftest.py
index 4016ff0..b3b4727 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1 +1,25 @@
-# Env var setup that must run before app.config is imported.
+from collections.abc import AsyncIterator
+
+import httpx
+import pytest
+from httpx import ASGITransport, AsyncClient
+
+from monitor_service.api import create_app
+from monitor_service.checker import CheckOutcome
+from monitor_service.config import Settings
+from monitor_service.models import CurrentStatus, MonitorState, utc_now
+
+
+class StubChecker:
+    async def check(self, monitor_id: object, url: str) -> CheckOutcome:
+        return CheckOutcome(url.split("?", 1)[0], CurrentStatus(
+            state=MonitorState.up, checked_at=utc_now(), latency_ms=1.25, http_status=204
+        ))
+
+
+@pytest.fixture
+async def client() -> AsyncIterator[AsyncClient]:
+    app = create_app(Settings(), checker=StubChecker())  # type: ignore[arg-type]
+    async with app.router.lifespan_context(app):
+        async with AsyncClient(transport=ASGITransport(app=app), base_url="http://test") as api:
+            yield api