secp256k1/ecdsa: Add tests for new R and S methods.

This adds a couple of additional checks to the sign and verify tests to
ensure the new R and S methods return the expected values.

dcrec/secp256k1/ecdsa/signature_test.go

@@ -1,5 +1,5 @@
 // Copyright (c) 2013-2016 The btcsuite developers
-// Copyright (c) 2015-2022 The Decred developers
+// Copyright (c) 2015-2023 The Decred developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -548,6 +548,20 @@ func TestSignAndVerify(t *testing.T) {
 			continue
 		}
 
+		// Ensure the R method returns the expected value.
+		gotSigR := gotSig.R()
+		if !gotSigR.Equals(wantSigR) {
+			t.Errorf("%s: unexpected R component -- got %064x, want %064x",
+				test.name, gotSigR.Bytes(), wantSigR.Bytes())
+		}
+
+		// Ensure the S method returns the expected value.
+		gotSigS := gotSig.S()
+		if !gotSigS.Equals(wantSigS) {
+			t.Errorf("%s: unexpected S component -- got %064x, want %064x",
+				test.name, gotSigS.Bytes(), wantSigS.Bytes())
+		}
+
 		// Ensure the produced signature verifies.
 		pubKey := privKey.PubKey()
 		if !gotSig.Verify(hash, pubKey) {