Just do not assign to variable.
@ -3216,7 +3216,7 @@ class LightningDTests(BaseLightningDTests):
# Create invoices
inv1 = l2.rpc.invoice(1000, 'inv1', 'inv1')
inv2 = l2.rpc.invoice(1000, 'inv2', 'inv2')
inv3 = l2.rpc.invoice(1000, 'inv3', 'inv3')
l2.rpc.invoice(1000, 'inv3', 'inv3')
# Start waiting on invoice 3
f3 = self.executor.submit(l2.rpc.waitinvoice, 'inv3')