Merge rust-bitcoin#3472: test: add test for new sign fn

88a35c8 test: add test for new sign fn (Chris Hyunhum Cho)

Pull request description:

  Follow up rust-bitcoin#3456.
  add test to verify the signature generated from newly added `sign` fn.

ACKs for top commit:
  apoelstra:
    ACK 88a35c8; successfully ran local tests; sorry, testing local CI changes..
  tcharding:
    ACK 88a35c8

Tree-SHA512: 8c457fbabf1ff86a9369934564874e78660f706714465731c185da16eff5c88a5e680c4373effbcc273394a5653edde9f559558917fee6e438b79bfee6f63b22

bitcoin/src/sign_message.rs

@@ -257,6 +257,7 @@ mod tests {
         let secp_sig = secp.sign_ecdsa_recoverable(&msg, &privkey);
         let signature = super::MessageSignature { signature: secp_sig, compressed: true };
 
+        assert_eq!(signature.to_string(), super::sign(&secp, message, privkey).to_string());
         assert_eq!(signature.to_base64(), signature.to_string());
         let signature2 = &signature.to_string().parse::<super::MessageSignature>().unwrap();
         let pubkey = signature2