What is the best way to unit test code that generates images? Say, for example, a class that generates a plot or a chart?
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What is the best way to unit test code that generates images? Say, for example, a class that generates a plot or a chart?
If this class uses a third party library to generate plots/charts (say matplotlib) then you can write tests for the methods that generate input for the the library. This will be fairly easy.
If the output is an image and you are interested in verifying its properties then you will have to dig deeper. External image attributes (size, height, format etc.) can be easily verified but others such as the actual contents of the image would be quite hard. IMHO that wouldn’t be worth the trouble.
If the output is non-binary (say SVG) then you can easily write tests to ensure that the output XML contains what you are looking for.