With test environment ready, we can move on and develop a simple bar chart very similar to what we have done in the Creating a bar chart recipe in Chapter 8, Chart Them Up, though this time in a test-driven fashion. You can see how the bar chart looks if you open the tdd-bar-chart.html page:

Test driven bar chart

By now we all know very well how to implement a bar chart using D3; however, building a bar chart is not the focus of this recipe. Instead, we want to show how we can build test cases every step of the way and verify automatically that our bar chart implementation is doing what it is supposed to do. The source code of this recipe was built using test driven development method; however, we will not show you every step in the TDD process due to limited scope in this book. Instead, we have grouped multiple steps into three larger sections with different focuses in this chapter and this recipe is the first step we take.