test: Check submitblock return values

test/functional/feature_nulldummy.py

@@ -111,7 +111,7 @@ class NULLDUMMYTest(BitcoinTestFramework):
         witness and add_witness_commitment(block)
         block.rehash()
         block.solve()
-        node.submitblock(block.serialize().hex())
+        assert_equal(None if accept else 'block-validation-failed', node.submitblock(block.serialize().hex()))
         if (accept):
             assert_equal(node.getbestblockhash(), block.hash)
             self.tip = block.sha256