For libpng (1.5.x) and libpng12:
Testing procedure, feel free to add to it.
If using it in the future, check that it's still valid with urpmq --whatrequires-recursive name_of_the_lib, especially for libpng12_0 because more and more packages switch to a newer libpng.
For libpng12, usually we test by opening some png files with xv, which depends on lib(64)png12_0. gcompris uses it too, indirectly, so try it.
For libpng15_15, lots of packages depend on it, including lots of games and viewers. Example : check that warmux and smc work well. Check that firefox can open a png file (don't forget to restart it after installing the update).
We also need to test png transformations, so use graphicsmagick to perform some transformations. Testing procedure for graphicsmagick : https://wiki.mageia.org/en/QA_procedure:GraphicsMagick
You can use sam2p (which links against libpng12_0) to convert a png to a PDF.
