I would very strongly recommend ' Test Pilots - The History of British Test Flying 1903 - 84 ' by Don Middleton, Collins Willow press, ISBN 0-00-218098-7.
The late D.Middleton was a pilot himself, and a very good author - this book is simply the best of it's type I have ever come across by a very wide margin.
It is never over-sensational, while comprehensively covering the story of how Test Flying developed, citing some quite remarkable feats and escapes ( and the inevitable tragedies ) while using them not just to entertain, but to drive home in a slightly understated way just what risks and achievements have been accomplished, both by aircrew and design & engineering staff - along with less successful projects.
The book is out of print, but fairly easily available at the usual places for quite reasonable amounts ( I have given secondhand copies to several people, who seem to agree with me ).
Perhaps an idea of my opinion of it is, if suffering a fire, it would be the first book I would grab to save, and I am constantly referring to it now I'm a museum volunteer !
' Tests of Character, Epic Flights by Legendary Test Pilots ' by the same author, Airlife, ISBN 1-85310-481-7 is very similar, and also very good, inevitably with some duplication - I'd say get both, but if only one, it has to be ' Test Pilots '.