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Asked: 2026-05-16T03:51:01+00:00

I’m using Java’s Graphics2D to generate a graphical representation of a graph. I’m also

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I’m using Java’s Graphics2D to generate a graphical representation of a graph. I’m also using ImageIO to write a PNG file. (ImageIO.write(image, "png", out);)

I’m wondering how should I write JUnit tests to test whether the generated graphics is what is expected. I could pre-generate the PNG files but what if the font is a bit different on a different machine?

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  1. Editorial Team

    You could try testing for specific, known features of the output e.g.:

    • It there a white pixel at (100,100)?
    • It the border completely black?
    • Is the image the expected size?

    And/or you could write tests for some “aggregate properties” that allow for some fuzziness in the results:

    • Does the image at least 90% match the reference image? (to allow for different fonts, antialiasing differences etc.)
    • Is the most common colour in the image equal to the background colour?
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