wallet: Minor testing of pay_index column.

tests/test_lightningd.py

@@ -334,6 +334,10 @@ class LightningDTests(BaseLightningDTests):
         assert b11['expiry'] == 3600
         assert b11['payee'] == l1.info['id']
 
+        # Check pay_index is null
+        outputs = l1.db_query('SELECT pay_index IS NULL AS q FROM invoices WHERE label="label";')
+        assert len(outputs) == 1 and outputs[0]['q'] != 0
+
     def test_invoice_expiry(self):
         l1,l2 = self.connect()
 
@@ -719,6 +723,10 @@ class LightningDTests(BaseLightningDTests):
         l1.rpc.pay(inv)
         assert l2.rpc.listinvoice('test_pay')[0]['complete'] == True
 
+        # Check pay_index is not null
+        outputs = l2.db_query('SELECT pay_index IS NOT NULL AS q FROM invoices WHERE label="label";')
+        assert len(outputs) == 1 and outputs[0]['q'] != 0
+
     def test_bad_opening(self):
         # l1 asks for a too-long locktime
         l1 = self.node_factory.get_node(options=['--locktime-blocks=100'])