Chapter 9. Testing the ezcGraph Component

Kore Nordmann


  • Overview of the ezcGraph component

  • Testing requirements for image-generating components

  • Using mock drivers to test the render class

  • Testing the output drivers

  • Working with SVG images

  • Working with bitmap images

  • Working with Adobe Flash graphics

In early 2007, I was asked to design and develop a component to generate graphs for the eZ Components project,[90] for several reasons. I already had lots of experience with image generation, I had already developed a chart library, and a chart library had been requested by the users of eZ Publish several times.

The requirements for components in the eZ Components were a bit different compared to the image libraries I developed before. The eZ Components project focuses on full backward compatibility, ease of use of all APIs, and stability. Backward compatibility and stability can be ensured by well-written unit tests, so all components are intended to be developed via test-driven methodology. Test-driven development of a component purely intended to generate images, which are nothing but binary data, resulted in some problems that had to be solved:

  • Test expectations are hard to craft beforehand.

  • The generated binary data may depend on aspects not defined in the test, such as library versions, dates, or some internal state in the library.

  • Proper comparison methods on binary data can be quite time-consuming.

This chapter shows how these problems were solved while developing the ...

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