To cite package ‘checkmate’ in publications use:

  Lang M (2017). “checkmate: Fast Argument Checks for Defensive R
  Programming.” _The R Journal_, *9*(1), 437-445.
  doi:10.32614/RJ-2017-028 <https://doi.org/10.32614/RJ-2017-028>.

A BibTeX entry for LaTeX users is

  @Article{checkmate,
    title = {{checkmate}: Fast Argument Checks for Defensive {R} Programming},
    author = {Michel Lang},
    journal = {The R Journal},
    year = {2017},
    doi = {10.32614/RJ-2017-028},
    pages = {437--445},
    volume = {9},
    number = {1},
  }