After reviving many bug reports, we recognized some of them spot unexpected EOF. The chop target was developed based on this recognition.

The chop target generates many input files from an existing input file under Units by truncating the existing input file at variety file positions.

$ make chop  LANGUAGES=LANG1[,LANG2,...]

It takes a long time, especially with VG=1, so this cannot be run under Travis CI. However, it is a good idea to run it locally.