I tried several solutions without any problem.

When I use "testthat" and run the exact same code in Rstudio, it works fine.

I run your code in RStudio and I got 'current' is not a factor'.
Not a kata issue.

The tests fail on Codewars:

"
Test Failed
actual not equal to expected.
'current' is not a factor
"

When I use "testthat" and run the exact same code in Rstudio, it works fine.

Same problem here. When I use the "testthat" library on my machine and run the exact same testing code it works fine. It throws the same error as you posted when I run it on Codewars.