feat(abstract-utxo): add test for signAndVerifyPsbt function

Tests the signAndVerifyPsbt function for transaction signing, verifying
that it correctly signs PSBTs and validates signatures for different
input types.

Issue: BTC-2806

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

Author: OttoAllmendinger

modules/abstract-utxo/test/unit/transaction/fixedScript/signPsbt.ts

@@ -0,0 +1,52 @@
+import assert from 'node:assert/strict';
+
+import * as utxolib from '@bitgo/utxo-lib';
+
+import { signAndVerifyPsbt } from '../../../../src/transaction/fixedScript/sign';
+
+function describeSignAndVerifyPsbt(acidTest: utxolib.testutil.AcidTest) {
+  describe(`${acidTest.name}`, function () {
+    it('should sign unsigned psbt to halfsigned', function () {
+      // Create unsigned PSBT
+      const psbt = acidTest.createPsbt();
+
+      // Set musig2 nonces for taproot inputs before signing
+      const sessionId = Buffer.alloc(32);
+      psbt.setAllInputsMusig2NonceHD(acidTest.rootWalletKeys.user, { sessionId });
+      psbt.setAllInputsMusig2NonceHD(acidTest.rootWalletKeys.bitgo, { deterministic: true });
+
+      // Sign with user key
+      const result = signAndVerifyPsbt(psbt, acidTest.rootWalletKeys.user, {
+        isLastSignature: false,
+      });
+
+      // Result should be a PSBT (not finalized)
+      assert(result instanceof utxolib.bitgo.UtxoPsbt, 'should return UtxoPsbt when not last signature');
+
+      // Verify that all wallet inputs have been signed by user key
+      result.data.inputs.forEach((input, inputIndex) => {
+        const { scriptType } = utxolib.bitgo.parsePsbtInput(input);
+
+        // Skip replay protection inputs (p2shP2pk)
+        if (scriptType === 'p2shP2pk') {
+          return;
+        }
+
+        // Verify user signature is present
+        const isValid = result.validateSignaturesOfInputHD(inputIndex, acidTest.rootWalletKeys.user);
+        assert(isValid, `input ${inputIndex} should have valid user signature`);
+      });
+    });
+  });
+}
+
+describe('signAndVerifyPsbt', function () {
+  // Create test suite with includeP2trMusig2ScriptPath set to false
+  // p2trMusig2 script path inputs are signed by user and backup keys,
+  // which is not the typical signing pattern and makes testing more complex
+  utxolib.testutil.AcidTest.suite({ includeP2trMusig2ScriptPath: false })
+    .filter((test) => test.signStage === 'unsigned')
+    .forEach((test) => {
+      describeSignAndVerifyPsbt(test);
+    });
+});