Handle should.throw() assertion with no argument properly

third_party/WebKit/LayoutTests/webaudio/resources/audit.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 
 /**
  * @fileOverview  WebAudio layout test utility library. Built around W3C's
  *                testharness.js. Includes asynchronous test task manager,
  *                assertion utilities.
  * @dependency    testharness.js
@@ skipping 252 matching lines @@
 
       let didThrowCorrectly = false;
       let passDetail, failDetail;
 
       try {
         // This should throw.
         this._actual();
         // Catch did not happen, so the test is failed.
         failDetail = '${actual} did not throw an exception.';
       } catch (error) {
-        if (this._expected === undefined) {
+        if (this._expected === null) {
+          // The expected error type was not given.
           didThrowCorrectly = true;
-          passDetail = '${actual} threw an exception of ' + error.name + '.';
+          passDetail = '${actual} threw ' + error.name + ': "'
+              + error.message + '".';
         } else if (error.name === this._expected) {
+          // The expected error type match the actual one.
           didThrowCorrectly = true;
-          passDetail = '${actual} threw ${expected} : "' + error.message + '".';
+          passDetail = '${actual} threw ${expected}: "'
+              + error.message + '".';
         } else {
           didThrowCorrectly = false;
           failDetail = '${actual} threw "' + error.name
             + '" instead of ${expected}.';
         }
       }
 
       return this._assert(didThrowCorrectly, passDetail, failDetail);
     }
 
@@ skipping 737 matching lines @@
         _logError('this test requires the explicit comparison with the '
             + 'expected result when it runs with run-webkit-tests.');
       }
 
       return new TaskRunner();
     }
 
   };
 
 })();