This is small idea , I am sharing a scenario to make you understand about this idea. Suppose we have written many apex class and ,for code coverage we also have written many test class. In some requirement we modified one class after that we will also modify test class for that class to mantain code coverage .It will be very difficult to search that test class in apex class . If all the test class in one location then we must search there and find it easily as compaired to previous one.
Salesforce has provided the specility that all triggers are in under ApexTrigger category, Like this If possible there should be a ApexTestClass category which contains all test class.
Salesforce Developer @ Mindfiresolitions