test: Throw error when -signetchallenge is non-hex

test/functional/feature_signet.py

@@ -76,6 +76,9 @@ class SignetBasicTest(BitcoinTestFramework):
         self.log.info("test that signet logs the network magic on node start")
         with self.nodes[0].assert_debug_log(["Signet derived magic (message start)"]):
             self.restart_node(0)
+        self.stop_node(0)
+        self.nodes[0].assert_start_raises_init_error(extra_args=["-signetchallenge=abc"], expected_msg="Error: -signetchallenge must be hex, not 'abc'.")
+        self.nodes[0].assert_start_raises_init_error(extra_args=["-signetchallenge=abc"] * 2, expected_msg="Error: -signetchallenge cannot be multiple values.")
 
 
 if __name__ == '__main__':