Combine test_subscription.py to test_pubsub.py

And add a bunch of tests for pubsub

tests/utils.py

@@ -13,6 +13,8 @@ async def connect(node1, node2):
     addr = node2.get_addrs()[0]
     info = info_from_p2p_addr(addr)
     await node1.connect(info)
+    assert node1.get_id() in node2.get_network().connections
+    assert node2.get_id() in node1.get_network().connections
 
 
 async def cleanup():
@@ -25,6 +27,7 @@ async def cleanup():
         with suppress(asyncio.CancelledError):
             await task
 
+
 async def set_up_nodes_by_transport_opt(transport_opt_list):
     nodes_list = []
     for transport_opt in transport_opt_list: