Add handle_graft test

tests/pubsub/test_gossipsub.py

@@ -98,6 +98,64 @@ async def test_leave():
     await cleanup()
 
 
+@pytest.mark.asyncio
+async def test_handle_graft(event_loop, monkeypatch):
+    num_hosts = 2
+    libp2p_hosts = await create_libp2p_hosts(num_hosts)
+
+    # Create pubsub, gossipsub instances
+    _, gossipsubs = create_pubsub_and_gossipsub_instances(libp2p_hosts, \
+                                                          SUPPORTED_PROTOCOLS, \
+                                                          10, 9, 11, 30, 3, 5, 0.5)
+
+    index_alice = 0
+    id_alice = str(libp2p_hosts[index_alice].get_id())
+    index_bob = 1
+    id_bob = str(libp2p_hosts[index_bob].get_id())
+    await connect(libp2p_hosts[index_alice], libp2p_hosts[index_bob])
+
+    # Wait 2 seconds for heartbeat to allow mesh to connect
+    await asyncio.sleep(2)
+
+    topic = "test_handle_graft"
+    # Only lice subscribe to the topic
+    await gossipsubs[index_alice].join(topic)
+
+    # Monkey patch bob's `emit_prune` function so we can
+    # check if it is called in `handle_graft`
+    event_emit_prune = asyncio.Event()
+    async def emit_prune(topic, sender_peer_id):
+        event_emit_prune.set()
+
+    monkeypatch.setattr(gossipsubs[index_bob], 'emit_prune', emit_prune)
+
+    # Check that alice is bob's peer but not his mesh peer
+    assert id_alice in gossipsubs[index_bob].peers_gossipsub
+    assert topic not in gossipsubs[index_bob].mesh
+    await gossipsubs[index_alice].emit_graft(topic, id_bob)
+
+    # Check that `emit_prune` is called
+    await asyncio.wait_for(
+        event_emit_prune.wait(),
+        timeout=1,
+        loop=event_loop,
+    )
+    assert event_emit_prune.is_set()
+
+    # Check that bob is alice's peer but not her mesh peer
+    assert topic in gossipsubs[index_alice].mesh
+    assert id_bob not in gossipsubs[index_alice].mesh[topic]
+    assert id_bob in gossipsubs[index_alice].peers_gossipsub
+    await gossipsubs[index_bob].emit_graft(topic, id_alice)
+
+    await asyncio.sleep(1)
+
+    # Check that bob is now alice's mesh peer
+    assert id_bob in gossipsubs[index_alice].mesh[topic]
+
+    await cleanup()
+
+
 @pytest.mark.asyncio
 async def test_dense():
     # Create libp2p hosts