For the R package source, R CMD check <pkg> runs R scripts under tests directory.

However, this directory is not included in binary package distribution. Some package users run tests after installing 

In this package, I put test codes under inst/unit_tests. Source code users call these test scripts via scripts under tests/ directory. Binary package users call these scripts, which are moved to unit_tests/ directory just under package root, from R function under R/ directory. 

