How write unit test for class which works with QImage

I have a program that apply a filter to an image. The code applies the filter to the image and to its frame. What should be the unit test for QImage, because I can't find a code example for QImage. And may be should be four tests?

class ImageChanger {
public:
    static QImage addMedianFilter(const QImage & image); //For one core Processor
    static QImage addMedianFilterMP(const QImage & image); //For multiple core Processor
    static QImage addMedianFilterTest(const QImage & image); //For test to MainWindow
    static QImage addMedianFilterFrame(const QImage & image); //For frame if there is multiple core Processor
};