Bug 1237961 - Assert.throws raises a TypeError exception when the "expected" parameter is an arrow function. r=mikedeboer

MozReview-Commit-ID: CyhD00Uwbwj

--HG--
extra : rebase_source : 24a80ca12bfdded82f4bc3487ee491defa60da7b

testing/modules/Assert.jsm

@@ -314,7 +314,10 @@ function expectedException(actual, expected) {
 
   if (instanceOf(expected, "RegExp")) {
     return expected.test(actual);
-  } else if (actual instanceof expected) {
+  // We need to guard against the right hand parameter of "instanceof" lacking
+  // the "prototype" property, which is true of arrow functions in particular.
+  } else if (!(typeof expected === "function" && !expected.prototype) &&
+             actual instanceof expected) {
     return true;
   } else if (expected.call({}, actual) === true) {
     return true;

testing/modules/tests/xpcshell/test_assert.js

@@ -208,6 +208,12 @@ function run_test() {
       return true;
     }
   });
+  // do the same with an arrow function
+  assert.throws(makeBlock(thrower, TypeError), err => {
+    if ((err instanceof TypeError) && /test/.test(err)) {
+      return true;
+    }
+  });
 
   function testAssertionMessage(actual, expected) {
     try {