从路由中返回无效的JSON。可能抛出了一个异常?

I've been working on adding JWT authentication to my Lumen API. Please bare in mind I am new to Lumen, API design and TDD. Before adding the authentication all of tests were passing. Honestly, everything seems to be working just fine except when I run phpunit. What's difficult to understand is when I run the same test in postman I have no issues, however when I dump the response in phpunit i get