Get symfony error or exception on cli for testing

While my unit test failed, it's only shows that the assertion does not meet my requirement.

for this kind of assertion,

$this->assertEquals(200, $client->getResponse()->getStatusCode());

the failed results is like:

Failed asserting that 500 matches expected 200.

How to get the exact error or exception that occured ?

I know I can dumping the response content like this

var_dump($client->getResponse()->getContent());

But it prints raw html that hard to read.

Thanks in advance.