Improve signmessages functional test

This patch improves branch coverage of the test, making sure a
message can not be verified with the wrong address or signature.

test/functional/signmessages.py

@@ -5,6 +5,7 @@
 """Test RPC commands for signing and verifying messages."""
 
 from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import assert_equal
 
 class SignMessagesTest(BitcoinTestFramework):
     def set_test_params(self):
@@ -14,20 +15,24 @@ class SignMessagesTest(BitcoinTestFramework):
     def run_test(self):
         message = 'This is just a test message'
 
-        # Test the signing with a privkey
-        privKey = 'cUeKHd5orzT3mz8P9pxyREHfsWtVfgsfDjiZZBcjUBAaGk1BTj7N'
+        self.log.info('test signing with priv_key')
+        priv_key = 'cUeKHd5orzT3mz8P9pxyREHfsWtVfgsfDjiZZBcjUBAaGk1BTj7N'
         address = 'mpLQjfK79b7CCV4VMJWEWAj5Mpx8Up5zxB'
-        signature = self.nodes[0].signmessagewithprivkey(privKey, message)
-
-        # Verify the message
+        expected_signature = 'INbVnW4e6PeRmsv2Qgu8NuopvrVjkcxob+sX8OcZG0SALhWybUjzMLPdAsXI46YZGb0KQTRii+wWIQzRpG/U+S0='
+        signature = self.nodes[0].signmessagewithprivkey(priv_key, message)
+        assert_equal(expected_signature, signature)
         assert(self.nodes[0].verifymessage(address, signature, message))
 
-        # Test the signing with an address with wallet
+        self.log.info('test signing with an address with wallet')
         address = self.nodes[0].getnewaddress()
         signature = self.nodes[0].signmessage(address, message)
-
-        # Verify the message
         assert(self.nodes[0].verifymessage(address, signature, message))
 
+        self.log.info('test verifying with another address should not work')
+        other_address = self.nodes[0].getnewaddress()
+        other_signature = self.nodes[0].signmessage(other_address, message)
+        assert(not self.nodes[0].verifymessage(other_address, signature, message))
+        assert(not self.nodes[0].verifymessage(address, other_signature, message))
+
 if __name__ == '__main__':
     SignMessagesTest().main()