Q:

Is it correct to say: I wish to day were being Saturday?

I found the above phrase as an answer for a question in TOEFL preparatory book but I think it is weird. The question was:

I wish today.......Saturday.  

was
is
were
were being

A:

If the review book you were using said that d) was correct then the book is wrong. Perhaps it is just a typo (those happen) but I'd be leery.
The correct answer is probably c) "were". This sentence is an "unreal conditional" - because, presumably, today is not Saturday. 
But I would say that this is a bad question (the one on the TOEFL, not your question about the TOEFL) because you could argue that a) "was" is correct because, in a sense, today might be Saturday. 
See grammarly

