To cite spTest in publications use:

Weller ZD (2018). “spTest: An R Package Implementing Nonparametric Tests of Isotropy.” Journal of Statistical Software, 83(4), pp. 1–24. doi: 10.18637/jss.v083.i04.

Corresponding BibTeX entry:

  @Article{,
    title = {{spTest}: An {R} Package Implementing Nonparametric Tests
      of Isotropy},
    author = {Zachary D. Weller},
    journal = {Journal of Statistical Software},
    year = {2018},
    volume = {83},
    number = {4},
    pages = {1--24},
    doi = {10.18637/jss.v083.i04},
  }