Revert "pytest: Remove the test_mutual_reconnect_race test"

This reverts commit 2fe4054.

tests/test_connection.py

@@ -4368,6 +4368,53 @@ def test_multichan(node_factory, executor, bitcoind):
     assert l2.rpc.listhtlcs(scid12)['htlcs'] == l1htlcs
 
 
+def test_mutual_reconnect_race(node_factory, executor, bitcoind):
+    """Test simultaneous reconnect between nodes"""
+    l1, l2 = node_factory.line_graph(2, opts={'may_reconnect': True,
+                                              'dev-no-reconnect': None})
+
+    def send_many_payments():
+        for i in range(20):
+            time.sleep(0.5)
+            inv = l2.rpc.invoice(
+                100 - i,  # Ensure prior chanhints don't block us
+                "label-" + str(i),
+                "desc"
+            )['bolt11']
+            try:
+                l1.rpc.pay(inv)
+            except RpcError:
+                pass
+
+    # Send a heap of payments, while reconnecting...
+    fut = executor.submit(send_many_payments)
+
+    for i in range(10):
+        try:
+            l1.rpc.disconnect(l2.info['id'], force=True)
+        except RpcError:
+            pass
+        time.sleep(1)
+        # Aim for both at once!
+        executor.submit(l1.rpc.connect, l2.info['id'], 'localhost', l2.port)
+        executor.submit(l2.rpc.connect, l1.info['id'], 'localhost', l1.port)
+
+    # Wait for things to settle down, then make sure we're actually connected.
+    # Naively, you'd think we should be, but in fact, two connects which race
+    # can (do!) result in both disconnecting, thinking the other side is more
+    # recent.
+    time.sleep(1)
+    if not only_one(l1.rpc.listpeers(l2.info['id'])['peers'])['connected']:
+        l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
+
+    # Now payments should finish!
+    fut.result(TIMEOUT)
+
+    wait_for(lambda: only_one(l1.rpc.listpeers(l2.info['id'])['peers'])['connected'])
+    inv = l2.rpc.invoice(100000000, "invoice4", "invoice4")
+    l1.rpc.pay(inv['bolt11'])
+
+
 def test_no_reconnect_awating_unilateral(node_factory, bitcoind):
     l1, l2 = node_factory.line_graph(2, opts={'may_reconnect': True})
     l2.stop()