It's a figure of speech. Looks like TFA clarified: > But the JWST was not designed or tested in a vacuum (pun only partially intended) It's not the clearest w

It's a figure of speech. Looks like TFA clarified: > But the JWST was not designed or tested in a vacuum (pun only partially intended) It's not the clearest writing, even though they are going for a joke. JWST was not "designed or tested in a vacuum" [in isolation without knowledge of prior art]". But it was designed for vacuum and its parts were tested in a vacuum, including I believe bringing the whole assembly down to cold vacuum. Designing in a literal vacuum sounds painful for the designers. :)