Merge pull request #2 from simonzack/master

fixes `.stack` on firefox

Author: keithamus

index.js

@@ -69,6 +69,8 @@ function AssertionError (message, _props, ssf) {
   ssf = ssf || arguments.callee;
   if (ssf && Error.captureStackTrace) {
     Error.captureStackTrace(this, ssf);
+  } else {
+    this.stack = new Error().stack;
   }
 }
 

test/test.js

@@ -13,6 +13,10 @@ suite(function (test, assert) {
     assert(empty.message === 'Unspecified AssertionError', 'w/o err.message');
   });
 
+  test('stack', function() {
+    assert(typeof new AssertionError().stack === 'string');
+  });
+
   test('custom properties', function () {
     var err = new AssertionError('good message', {
         name: 'ShouldNotExist'