Jacob's examples are great. Just for grins here is another approach. This should be about the same for performance but is a bit simpler to understand in my opinion.
select p.PatientName
from #Patient P
INNER JOIN #Test T ON T.TestID = P.TESTID
group by p.PatientName
having COUNT(distinct t.TestID) = 2
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Understanding and Using APPLY (Part 1) - http://www.sqlservercentral.com/articles/APPLY/69953/
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