eNotes offers many quizzes for a variety of literature titles. The current quiz list has over 130 short answer quizzes. There are more than 800 multiple choice quizzes as well. Each of the quizzes on this sight has been created by an expert on that text, so you can be confident that using them is a solid way to check reading comprehension. From the eNotes homepage, click the "Teachers" icon in the top navigation. That will open a drop down menu. Select "Literature Quizzes," and the entire quiz list will be displayed. Unfortunately, no quizzes exist yet on eNotes for this wonderful book. eNotes does offer an in-depth study guide for this title as well as providing chapter summaries, theme discussions, and character analyses.
I'm certain that tests and quizzes do exist online for this book; however, I would caution using them. Many quiz websites allow anybody and everybody to create and post a quiz, and the website doesn't necessarily vet and fact check the quiz for accuracy. My recommendation is to create your own chapter tests for the book. Create a mixture of multiple choice and short answer questions. Have some of the questions be identical from chapter to chapter. For example, ask how Holling's relationship with Mrs. Baker is going in each chapter. This is pivotal to understanding Holling's growth over the course of the book. By creating your own test and providing your own answers, you are forcing yourself to really know, understand, and review the text. This is more beneficial than taking someone else's test about the book.