1. Save this image to disk:

    If this isn't a yellow-blue gradient, then fail.

  2. Run pngcheck -v filename.png
  3. If the output reports any errors, then fail.
  4. If the output contains any "color space information" chunks, then fail. (Invalid chunks include cHRM, gAMA, iCCP, sBIT, sRGB. Safe chunks include IHDR, IDAT, IEND.)
  5. Otherwise, pass.

Test data: