Improve assertion handling when comparison causes failure via coercion

harness/assert.js

@@ -27,7 +27,12 @@ assert._isSameValue = function (a, b) {
 };
 
 assert.sameValue = function (actual, expected, message) {
-  if (assert._isSameValue(actual, expected)) {
+  try {
+    if (assert._isSameValue(actual, expected)) {
+      return;
+    }
+  } catch (error) {
+    $ERROR(message + ' (_isSameValue operation threw) ' + error);
     return;
   }
 

test/intl402/Segmenter/constructor/subclass.js

@@ -0,0 +1,28 @@
+// Copyright 2018 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-Intl.Segmenter
+description: The prototype of the Intl.Segmenter constructor is %FunctionPrototype%.
+info: |
+    Unless specified otherwise in this document, the objects, functions, and constructors described in this standard are subject to the generic requirements and restrictions specified for standard built-in ECMAScript objects in the ECMAScript 2019 Language Specification, 10th edition, clause 17, or successor.
+    Unless otherwise specified every built-in function object has the %FunctionPrototype% object as the initial value of its [[Prototype]] internal slot.
+features: [Intl.Segmenter]
+---*/
+
+class CustomSegmenter extends Intl.Segmenter {
+  constructor(...args) {
+    super(...args);
+    this.isCustom = true;
+  }
+}
+
+let cs = new CustomSegmenter();
+
+assert.sameValue(Object.getPrototypeOf(CustomSegmenter), Intl.Segmenter, 'Object.getPrototypeOf(CustomSegmenter) returns the value of `Intl.Segmenter` (undefined)');
+assert.sameValue(Object.getPrototypeOf(CustomSegmenter.prototype), Intl.Segmenter.prototype, 'Object.getPrototypeOf(CustomSegmenter.prototype) returns the value of `Intl.Segmenter.prototype` (undefined)');
+assert.sameValue(
+  cs instanceof Intl.Segmenter,
+  'CustomSegmenter instance is instanceof Intl.Segmenter',
+  'The result of `(cs instanceof Intl.Segmenter)` is "CustomSegmenter instance is instanceof Intl.Segmenter"'
+);