The book 'Testimony to Hilaire Belloc' is a work co-written by Eleanor and Reginald Jebb. This book is a biography that provides personal insights and testimonies into the life and character of the famous writer Hilaire Belloc. It offers a more intimate and subjective view of Belloc, different from the standard academic biography. The main focus of this book is to document various aspects of Hilaire Belloc's life, perhaps including his personality, strong Catholic faith, his love of the county of Sussex in England, and his working methods as a writer. In short, this book serves as a personal history and tribute to Hilaire Belloc, written by those who were close to him, sharing their memories and views of him.