phpunit无法断言两个数组相等,但没有显示出差异

这是phpunit说的:

1) Asgard\Entity\Tests\EntityTest::testToArray
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
 Array (
     'id' => null
     'title' => 'Test Title'
     'content' => 'Test Content'
     'published' => 2015-03-04T11:19:50+0000
     'comments' => Array (
         0 => Array (
             'id' => null
             'content' => 'foo'
             'published' => 2015-03-04T11:19:50+0000
             'another_property' => null
             'news' => null
         )
         1 => Array (
             'id' => null
             'content' => 'bar'
             'published' => 2015-03-04T11:19:50+0000
             'another_property' => null
             'news' => null
         )
         2 => Array (
             'id' => null
             'content' => 'baz'
             'published' => 2015-03-04T11:19:50+0000
             'another_property' => null
             'news' => null
         )
     )
     'another_property' => null
 )

https://travis-ci.org/asgardphp/asgard/jobs/53029084

"预期"和"实际"之间没有区别.测试通常会通过,但有时会失败.