r - Unit testing with `testthat` on functions that write/read files, or a Fortran error -

what best way make unit testing testthat on functions read , write files?

apologies asking complicated question, not sure wrong here.

i have implemented number of functions in fortran, reads , writes files. compiled in r package cf. writing r extension manual. unit testing testthat generates random content written temporary files tempfile(). running r cmd check on r package works on local windows machine.

running r-devel fails because cannot detect rtools r-3.5.0 (devel). submitted win-builder.

http://win-builder.r-project.org/ fails following error:

  @ line 9 of file auxil.f95 fortran runtime error: actual string length shorter declared 1 dummy argument 'fn' (96/255) 

with corresponding fortran source:

subroutine get_nlines(fn, nlines, stat) !line 9   implicit none    !! arguments   character(255), intent(in) :: fn   integer, intent(out) :: nlines, stat    !! local variables   character(len=1) :: 1    nlines = 0   open(40, file=fn, status='old')       read(40, *, iostat=stat) 1     if (stat /= 0) exit     nlines = nlines + 1   end   close(40)  end subroutine 

the fortran code stored in src subdirectory of r package, , called with

get_nlines <- function(fn) {   stopifnot(file.exists(fn))   res <- .fortran('get_nlines', fn=as.character(fn), nlines=integer(1), stat=integer(1))   if (res$nlines == 0 & res$stat != 0) {     warning(paste0('get_nlines did not read lines; iostat error ', res$stat, '.'))     return(structure(na, code=res$stat))   }   res$nlines } 

so there is. don't know if fortran code wrong, or if it's occurs on win-builder server.

"i don't know if fortran code wrong" still don't understand question if code have shown "the" code or if inside r package using.

if fortran code speaking (you didn't show else), should try character(*) instead of character(255), because there no apparent reason exact fixed length 255. error message complains about, fn not 255 chars long require in get_nlines().