You don't need to join the testing team to write a hardware review. Or am I misunderstanding your intent? The testing team does the quality assurance tests on new ISOs before they are released for beta testing. Those tests are specific and about the ISO itself; they are not about hardware compatibility or issues. If you click on any of the ISOs here
https://community.linuxmint.com/iso you can view the test cases that the QA testing team does.
So if you just want to write a hardware review for how well a specific Linux Mint version works with your laptop, you just need to register an account on the Community website and then on its My Places > My Hardware menu you can click the button to write a new hardware review.