feat(utxo-core): add deterministic test fixtures for PayGo address proof

Replace the dynamic test fixture generation with deterministic values.
Use fixed entropy for consistent test outputs and add verification tests
to validate the structure and content of test fixtures.

Issue: BTC-290

Co-authored-by: llm-git <[email protected]>

Author: OttoAllmendinger

modules/utxo-core/test/paygo/psbt/payGoAddressProof.ts

@@ -13,8 +13,6 @@ import {
   psbtOutputIncludesPaygoAddressProof,
   verifyPayGoAddressProof,
 } from '../../../src/paygo/psbt/payGoAddressProof';
-import { generatePayGoAttestationProof } from '../../../src/testutil/generatePayGoAttestationProof.utils';
-import { trimMessagePrefix } from '../../../src/testutil/trimMessagePrefix';
 import { signMessage } from '../../../src/bip32utils';
 import { NIL_UUID } from '../../../src/paygo/attestation';
 
@@ -45,19 +43,64 @@ export const addressToVerify = utxolib.address.toBase58Check(
   utxolib.networks.bitcoin
 );
 
-// this should be retuning a Buffer
-export const addressProofBuffer = generatePayGoAttestationProof(NIL_UUID, Buffer.from(addressToVerify));
-export const addressProofMsgBuffer = trimMessagePrefix(addressProofBuffer);
-// We know that that the entropy is a set 64 bytes.
-export const addressProofEntropy = addressProofMsgBuffer.subarray(0, 65);
+// Fixed entropy for deterministic test fixtures (64 bytes of 0x00)
+export const addressProofEntropy = Buffer.alloc(64, 0x00);
 
-// signature with the given msg addressProofBuffer
+// Create the message buffer manually with our fixed entropy
+const addressBuffer = Buffer.from(addressToVerify);
+const uuidBuffer = Buffer.from(NIL_UUID);
+export const addressProofMsgBuffer = Buffer.concat([addressProofEntropy, addressBuffer, uuidBuffer]);
+
+// signature with the given msg addressProofMsgBuffer
 export const sig = signMessage(addressProofMsgBuffer, attestationPrvKey!, network);
 
 function getTestPsbt() {
   return utxolib.testutil.constructPsbt(psbtInputs, psbtOutputs, network, rootWalletKeys, 'unsigned');
 }
 
+describe('test fixtures', () => {
+  it('should have expected test fixture values', () => {
+    // Address fixture - derived from backup key
+    assert.strictEqual(addressToVerify, '1CdWUVacSQQJ617HfuNWByGiisEGXGNx2c');
+
+    // Entropy fixture - fixed 64 bytes of zeros for deterministic testing
+    assert.strictEqual(
+      addressProofEntropy.toString('hex'),
+      '0000000000000000000000000000000000000000000000000000000000000000' +
+        '0000000000000000000000000000000000000000000000000000000000000000'
+    );
+    assert.strictEqual(addressProofEntropy.length, 64);
+
+    // Signature fixture - Bitcoin message signature (65 bytes with recovery ID)
+    assert.strictEqual(
+      sig.toString('hex'),
+      '1fd62abac20bb963f5150aa4b3f4753c5f2f53ced5183ab7761d0c95c2820f6b' +
+        'b722b6d0d9adbab782d2d0d66402794b6bd6449dc26f634035ee388a2b5e7b53f6'
+    );
+    assert.strictEqual(sig.length, 65);
+
+    // Public key fixture - compressed secp256k1 public key (33 bytes)
+    assert.strictEqual(
+      attestationPubKey.toString('hex'),
+      '02456f4f788b6af55eb9c54d88692cadef4babdbc34cde75218cc1d6b6de3dea2d'
+    );
+    assert.strictEqual(attestationPubKey.length, 33);
+
+    // Message buffer structure: [ENTROPY][ADDRESS][UUID]
+    // Total length: 64 (entropy) + 34 (address) + 36 (UUID) = 134
+    assert.strictEqual(addressProofMsgBuffer.length, 134);
+
+    // Verify message components
+    const entropy = addressProofMsgBuffer.subarray(0, 64);
+    const address = addressProofMsgBuffer.subarray(64, 98);
+    const uuid = addressProofMsgBuffer.subarray(98, 134);
+
+    assert.strictEqual(entropy.toString('hex'), addressProofEntropy.toString('hex'));
+    assert.strictEqual(address.toString(), addressToVerify);
+    assert.strictEqual(uuid.toString(), NIL_UUID);
+  });
+});
+
 describe('addPaygoAddressProof and verifyPaygoAddressProof', () => {
   function getPayGoProprietaryKey(proprietaryKeyVals: KeyValue[]) {
     return proprietaryKeyVals