pkgload::system.file is too tolerant

[oganm]

On a testing environment if one does

devtools::load_all()
system.file('inst/filename', package="packageName", mustWork = TRUE)

devtools::system.file will happily return the file. However this is not the correct syntax.

If I do

devtools::install('.')
library(pacakgeName)
system.file('inst/filename', package="packageName", mustWork = TRUE)

I will get no file found because of the trailing inst.