Add coverage for abrupt completion from ToNumber via ToUint16 in String.fromCharCode

test/built-ins/String/fromCharCode/touint16-tonumber-throws-bigint.js

@@ -0,0 +1,26 @@
+// Copyright (C) 2026 Hyunjoon Kim. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-string.fromcharcode
+description: >
+    String.fromCharCode propagates abrupt completion from ToNumber when argument is BigInt via ToUint16.
+info: |
+    String.fromCharCode ( ..._codeUnits_ )
+
+    2. For each element _next_ of _codeUnits_, do
+      a. Let _nextCU_ be the code unit whose numeric value is ℝ(? ToUint16(_next_)).
+
+    ToUint16 ( _argument_ )
+
+    1. Let _number_ be ? ToNumber(_argument_).
+
+    ToNumber ( _argument_ )
+
+    2. If _argument_ is either a Symbol or a BigInt, throw a *TypeError* exception.
+features: [BigInt]
+---*/
+
+assert.throws(TypeError, function () {
+  String.fromCharCode(0n);
+}, "ToNumber throws when argument is BigInt, and String.fromCharCode must propagate it.");

test/built-ins/String/fromCharCode/touint16-tonumber-throws-valueof.js

@@ -0,0 +1,27 @@
+// Copyright (C) 2026 Hyunjoon Kim. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-string.fromcharcode
+description: >
+    String.fromCharCode propagates abrupt completion from ToNumber via ToUint16. (ToPrimitive/valueOf throws)
+info: |
+    String.fromCharCode ( ..._codeUnits_ )
+
+    2. For each element _next_ of _codeUnits_, do
+      a. Let _nextCU_ be the code unit whose numeric value is ℝ(? ToUint16(_next_)).
+
+    ToUint16 ( _argument_ )
+
+    1. Let _number_ be ? ToNumber(_argument_).
+
+    ToNumber ( _argument_ )
+
+    8. Let _primValue_ be ? ToPrimitive(_argument_, ~number~).    
+---*/
+
+assert.throws(Test262Error, function () {
+  String.fromCharCode({
+    valueOf: function () { throw new Test262Error(); }
+  });
+}, "ToNumber throws when its argument's ToPrimitive step calls a throwing valueOf, and String.fromCharCode must propagate it.");