This both excludes the autotests and tests subdirs if the user sets
BUILD_TESTING off, and makes sure we do not run tests for formats that
were not built due to dependencies not being found.
REVIEW: 115504
Two main tests: read the file and compare to a given image (loaded from
png), and write a file out and compare to a previously-written image.
The write test in particular is kind of fragile, but it should help
catch some errors where a code change was not intended to affect the
output of the plugin.
Tests are included for all the writable formats, as well as every
readable format that GIMP can write to (and so I could easily get an
example of).
REVIEW: 115430
src/imageformats/CMakeLists.txt is now much clearer and more consistent.
Also, removed an unnecessary/unimplemented method from exr.cpp.
REVIEW: 115120
