[Refactor] Avoid setting message property on primitives; use strict mode to catch this

Author: aredridel

lib/test.js

@@ -1,3 +1,5 @@
+'use strict';
+
 var deepEqual = require('deep-equal');
 var defined = require('defined');
 var path = require('path');
@@ -497,7 +499,7 @@ Test.prototype['throws'] = function (fn, expected, msg, extra) {
         fn();
     } catch (err) {
         caught = { error: err };
-        if ((err != null) && (!isEnumerable(err, 'message') || !has(err, 'message'))) {
+        if (Object(err) === err && (!isEnumerable(err, 'message') || !has(err, 'message'))) {
             var message = err.message;
             delete err.message;
             err.message = message;