Tuberculosis test required for 2 year standard visitor visa or not

Hi all,
I'm applying the standard visitor visa for 2 years for my parents and I'm quite unsure about the tuberculosis test. It said we would need to do it if "stay over 6 months", however it's only 6 month max per stay if having the standard visitor visa.
So would that mean my parent do not need to do this test if I understand the requirement correctly?
There is no requirement in the checklist but I would like to make sure that we are not missing anything important.
Thanks for your advice.

Not required for visitor visas.

Thanks a lot for your help CR001. Greatly appreciated.