It seems that a lot of books in the market on testing deal with the theoretical background of designing large scale tests on the institutional level. Those sorts of books are not so useful for the practicing teacher who is looking for a little guidance on improving their test writing skills for daily classes. This book is written with that teacher in mind. It doesn't overload the reader with loads of statistics, but if you are interested in the statistical basis of the ideas presented in this book, there is a section on statistics in the appendix.
Basically, this book is divided into three sections. The first section covers the different types of test a teacher might want to give and the differences between those types. The second part delves into the theory of validity and realiability, but doesn't overwhelm the reader with loads of numbers and figures. The third part goes into how to test different skills. The attitude the author takes toward testing is that a test should focus on one of the four basic skills: speaking, reading, writing, or listening. Grammar and vocabulary, he claims, are not ends in themselves, but merely components of the four basic skills, so they don't need to be given much emphasis in testing. I thought that was an interesting idea.
If you're a teacher looking for a book to help you with your test writing skills, I can recommend this one.