One book after reading the nuts and bolts of test pilot’s books is to turn to Tony Blackman’s “Flight Testing to Win”.
The book’s blurb says: ‘Tony has recorded some of his own experiences in his book 'Flight Testing to Win' where he explains that safety costs money and that an aircraft need only just meet the relevant design requirements. Tony Blackman tells about testing the V Bombers, selling the Avro 748 around the world and there is a chapter on flying with the legendary Howard Hughes in England.’
That's a reasonable enough description, but speaking as the end-user, mine is a bit more direct: a very good read, goos stories, and very realistic about the business, and chock-full of the commercial realities of being a test pilot. It’s also pleasant just to read (like his other books) when you’re not looking to get too serious. Easy to find by googling his name.