When MIME codecs were imported from KMime in 5c66308c, this unit test was missed to be readded to the build. Also was it not completely ported to the new API as well as had dropped some tests for the used charsets compared to the original file, which are readded here.
The file also contained an encoding issue added to the original file rfc2047test.cpp in KMime's commit pim/kmime@d8d4d0ed which is also fixed.
One test shows a regression though, marked with a TODO for now.
See also https://mail.kde.org/pipermail/kde-frameworks-devel/2014-November/020229.html for review of original move importing the code.