'This function creates an image that can be used to test vis functions.
It makes an image composed of four colored rectangles.
Returns:
colorful test numpy array image.'

def create_colorful_test_image(self):

    ch255 = np.full([100, 200, 1], 255, dtype=np.uint8)
    ch128 = np.full([100, 200, 1], 128, dtype=np.uint8)
    ch0 = np.full([100, 200, 1], 0, dtype=np.uint8)
    imr = np.concatenate((ch255, ch128, ch128), axis=2)
    img = np.concatenate((ch255, ch255, ch0), axis=2)
    imb = np.concatenate((ch255, ch0, ch255), axis=2)
    imw = np.concatenate((ch128, ch128, ch128), axis=2)
    imu = np.concatenate((imr, img), axis=1)
    imd = np.concatenate((imb, imw), axis=1)
    image = np.concatenate((imu, imd), axis=0)
    return image
