Laravel: Object of class `AssertableJsonString` could not be converted to string

ErrorException: Object of class Illuminate\Testing\AssertableJsonString could not be converted to string

Issue

Laravel decodes JSON responses into an AssertableJsonString for ease of testing APIs. However, you may be using this object in a capacity where PHP is attempting to convert it to a string.

Solution

The most likely cause of this error relates to a change in Laravel 8, where the decodeResponseJson no longer accepts an argument. Due to the dynamic nature of PHP, you may still call this method with an argument but it will return the entire JSON object, instead of the value for the passed key.

If you are calling decodeResponseJson with an argument, you should update your code to use json instead. If you are not using decodeResponseJson and receiving this error, you are likely passing the entire AssertableJsonString object where a string is expected.