Although it’s impossible to directly test the result of a rendering algorithm, as the result is an image, there’s always biases of each pixel value, according to the algorithm and hardware which determine the accuracy of numbers, we can use unit test to test the atomic functions of the rendering algorithm. For example, the transformation functions are testable. Randomness, such as Russian Roulette in ray marching, can be visualized so we can see if the distribution is even, or use Fourier Transformation to see if the variation is small enough.