Add fixtures for pubsub and router

And a starting `test_pubsub.py`

tests/pubsub/test_pubsub.py

@@ -0,0 +1,11 @@
+import pytest
+
+
+@pytest.mark.asyncio
+async def test_test(pubsubs_fsub):
+    topic = "topic"
+    data = b"data"
+    sub = await pubsubs_fsub[0].subscribe(topic)
+    await pubsubs_fsub[0].publish(topic, data)
+    msg = await sub.get()
+    assert msg.data == data