test: bootstrap backend pytest infrastructure with sanity tests

backend/tests/conftest.py

@@ -0,0 +1,8 @@
+"""Shared pytest fixtures for backend tests."""
+import asyncio
+import pytest
+
+
+@pytest.fixture
+def anyio_backend():
+    return "asyncio"

backend/tests/test_sanity.py

@@ -0,0 +1,12 @@
+"""Sanity test to verify pytest infrastructure works."""
+import asyncio
+import pytest
+
+
+def test_sync_sanity():
+    assert 1 + 1 == 2
+
+
+async def test_async_sanity():
+    await asyncio.sleep(0)
+    assert True