feat: add tests for maxWeightToSatisfy

Issue: BTC-1460

Author: OttoAllmendinger

packages/wasm-miniscript/test/fixedScriptToDescriptor.ts

@@ -8,6 +8,48 @@ const scriptTypes = ["p2sh", "p2shP2wsh", "p2wsh"] as const;
 const scope = ["external", "internal"] as const;
 const index = [0, 1, 2];
 
+/** Get the expected max weight to satisfy the descriptor */
+function getExpectedMaxWeightToSatisfy(scriptType: utxolib.bitgo.outputScripts.ScriptType2Of3) {
+  switch (scriptType) {
+    case "p2sh":
+      return 256;
+    case "p2shP2wsh":
+      return 99;
+    case "p2wsh":
+      return 64;
+    default:
+      throw new Error("unexpected script type");
+  }
+}
+
+/** Compute the total size of the input, including overhead */
+function getTotalInputSize(vSize: number) {
+  const sizeOpPushData1 = 1;
+  const sizeOpPushData2 = 2;
+  return (
+    32 /* txid */ +
+    4 /* vout */ +
+    4 /* nSequence */ +
+    (vSize < 255 ? sizeOpPushData1 : sizeOpPushData2) +
+    vSize
+  );
+}
+
+/** Get the full expected vSize of the input including overhead */
+function getExpectedVSize(scriptType: utxolib.bitgo.outputScripts.ScriptType2Of3) {
+  // https://github.com/BitGo/BitGoJS/blob/master/modules/unspents/docs/input-costs.md
+  switch (scriptType) {
+    case "p2sh":
+      return 298;
+    case "p2shP2wsh":
+      return 140;
+    case "p2wsh":
+      return 105;
+    default:
+      throw new Error("unexpected script type");
+  }
+}
+
 function runTest(
   scriptType: utxolib.bitgo.outputScripts.ScriptType2Of3,
   index: number,
@@ -24,11 +66,16 @@ function runTest(
       scriptType,
     ).scriptPubKey;
 
-    it("descriptor should have expected format", function () {
-      const descriptor = Descriptor.fromString(
+    let descriptor: Descriptor;
+
+    before(function () {
+      descriptor = Descriptor.fromString(
         getDescriptorForScriptType(rootWalletKeys, scriptType, scope),
         "derivable",
       );
+    });
+
+    it("descriptor should have expected format", function () {
       const [x1, x2, x3] = rootWalletKeys.triple.map((xpub) => xpub.neutered().toBase58());
       if (scriptType === "p2sh" && scope === "external") {
         // spot check
@@ -49,16 +96,23 @@ function runTest(
     });
 
     it("address should match descriptor", function () {
-      const scriptFromDescriptor = Buffer.from(
-        Descriptor.fromString(
-          getDescriptorForScriptType(rootWalletKeys, scriptType, scope),
-          "derivable",
-        )
-          .atDerivationIndex(index)
-          .scriptPubkey(),
-      );
+      const scriptFromDescriptor = Buffer.from(descriptor.atDerivationIndex(index).scriptPubkey());
       assert.deepStrictEqual(scriptUtxolib.toString("hex"), scriptFromDescriptor.toString("hex"));
     });
+
+    it("should have expected weights", function () {
+      assert.ok(Number.isInteger(descriptor.maxWeightToSatisfy()));
+      const vSize = Math.ceil(descriptor.maxWeightToSatisfy() / 4);
+      console.log(
+        scriptType,
+        "scriptLength",
+        descriptor.atDerivationIndex(0).encode().length,
+        "vSize",
+        vSize,
+      );
+      assert.equal(vSize, getExpectedMaxWeightToSatisfy(scriptType));
+      assert.equal(getTotalInputSize(vSize), getExpectedVSize(scriptType));
+    });
   });
 }