question: public static List < List < File > > findJavaFilesPerDirectory ( File parent , String ... dirNames ) { List < List < File > > filesPerDirectory = new ArrayList < > ( ) ; for ( String dirName : dirNames ) { File dir = new File ( parent , dirName ) ; if ( dir . isDirectory ( ) ) { filesPerDirectory . addAll ( findJavaTestFilesInDirectory ( dir ) ) ; } } return filesPerDirectory ; }
target:  Returns a list where each item is a list of Java files, excluding any skip tests, for each directory given by dirName and also a list for any subdirectory.