Testing just the goat you buy or a kid will not stop you introducing Johne's disease into your herd as tests turn positive around the time the goat is infectious. There is no test that is accurate in a kid. Get copies of the last few years annual negative tests and ask about biosecurity in between these tests.
Buying goats from herds in the Market Assurance Scheme is the safest way. Dr Sandra Baxendell is a MAP accredited veterinarian & can guide you through this process and collect the samples. Quotes provided.
All the latest research summarized in a well-organized and easy to read format.
Check out this great video about Johne's disease in goats