This book comes with a bundled example application, which you can find on GitHub.
Most of the code samples included in the book come directly from commits in the example application. Several chapters link to the full commits for related changes. At any point, you can check out the application locally and check out those commits to explore solutions in progress.
For some solutions, the entire change is not included in the chapter for the sake of focus and brevity. However, you can see every change made for a solution in the example commits, including tests.
Make sure to take a look at the application's README, as it contains a summary of the application and instructions for setting it up.