pytest: check nonstandard onion generation.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tests/test_pay.py

@@ -2816,7 +2816,8 @@ def test_partial_payment_htlc_loss(node_factory, bitcoind):
 def test_createonion_limits(node_factory):
     l1, = node_factory.get_nodes(1)
     hops = [{
-        "pubkey": "02eec7245d6b7d2ccb30380bfbe2a3648cd7a942653f5aa340edcea1f283686619",
+        # privkey: 41bfd2660762506c9933ade59f1debf7e6495b10c14a92dbcd2d623da2507d3d
+        "pubkey": "0266e4598d1d3c415f572a8488830b60f7e744ed9235eb0b1ba93283b315c03518",
         "payload": "00" * 228
     }, {
         "pubkey": "0324653eac434488002cc06bbfb7f10fe18991e35f9fe4302dbea6d2353dc0ab1c",
@@ -2840,6 +2841,20 @@ def test_createonion_limits(node_factory):
         hops[0]['payload'] += '01'
         l1.rpc.createonion(hops=hops, assocdata="BB" * 32)
 
+    # But with a larger onion, it will work!
+    oniontool = os.path.join(os.path.dirname(__file__), "..", "devtools", "onion")
+    onion = l1.rpc.createonion(hops=hops, assocdata="BB" * 32, onion_size=1301)['onion']
+
+    # Oniontool wants a filename :(
+    onionfile = os.path.join(l1.daemon.lightning_dir, 'onion')
+    with open(onionfile, "w") as f:
+        f.write(onion)
+
+    subprocess.check_output(
+        [oniontool, '--assoc-data', "BB" * 32,
+         'decode', onionfile, "41bfd2660762506c9933ade59f1debf7e6495b10c14a92dbcd2d623da2507d3d"]
+    )
+
 
 @pytest.mark.developer("needs use_shadow")
 def test_blockheight_disagreement(node_factory, bitcoind, executor):