Bug 1061813 - Added a check to test whether this.currentTest.scope.test is a function. r=jmaher

testing/mochitest/browser-test.js

@@ -766,8 +766,10 @@ Tester.prototype = {
         var result = this.currentTest.scope.generatorTest();
         this.currentTest.scope.__generator = result;
         result.next();
-      } else {
+      } else if (typeof this.currentTest.scope.test == "function") {
         this.currentTest.scope.test();
+      } else {
+        throw "This test didn't call add_task, nor did it define a generatorTest() function, nor did it define a test() function, so we don't know how to run it.";
       }
     } catch (ex) {
       let isExpected = !!this.SimpleTest.isExpectingUncaughtException();