Introduction

Whenever we program as a professional programmer it is always important to test the program we write in order to make sure it functions as designed and produces the expected outcome. D3 data visualization mainly consists of JavaScript programs hence just like any other program we write, data visualization needs to be tested to make sure it represents the underlying data accurately. Obviously, we can perform our validation through visual examination and manual testing, which is always a critical part of the process of building data visualization since visual observation gives us a chance to verify not only the correctness, but also the aesthetics, usability, and many other useful aspects. However, manual visual inspection can be quite subjective, therefore, in this chapter we will focus our effort on automated unit testing. Visualization well covered by unit tests can free the creator from the manual labor of verifying correctness by hand, additionally allowing the creator...