# Dear _R_CHECK_TESTS_NLINES_, where were you these years?

### Yihui Xie / 2017-12-15

When running R CMD check, I often cry a little upon “Last 13 lines of output” in the log, because 13 lines is often not enough for me to figure out why tests failed. Today I was tortured by this problem again (it is particularly painful when tests only fail on Travis CI but not locally1), and could no longer stand it. I desperately wanted to see more lines of output. After some Google searches, I didn’t find an answer, so in the spirit of “Luke, use the force source!“, I searched in the base R source (Winston’s r-source repo), and finally found this line in tools/R/check.R. Bingo! The magic number 13 is controlled by the environment variable named _R_CHECK_TESTS_NLINES_. Then I went to the R Internals manual, and found it had been documented there.

After I set _R_CHECK_TESTS_NLINES_=0, I was able to see the full output (instead of the truncated version), and finally figured out what was wrong.

1. I’m aware of the debug mode on Travis, and just don’t bother sending the email request.