How to ensure english error messages in testthat unit tests - r

Question

I have a lot of unit tests using the testthat package that expect english error messages.
If other developer run the tests on a computer configured for a non-english locale the error message are emitted in a different language and my tests fail.
How can I initialize testthat to change the language settings only during the test run-time without manually or permanently changing the language or test environment from outside of R (like e. g. proposed here: in R how to get error messages in english)?
library(testthat)
# works only in english locales...
expect_error(log("a"), "non-numeric argument to mathematical function", fixed = TRUE)
Edit 1: Changing the locale during run-time does not change the language of the error messages (using Ubuntu and OSX High Sierra):
Sys.setlocale( locale = "en_US.UTF-8")
Sys.getlocale() # en_US is active now but messages are still in another language
Edit 2: It seems that Sys.setenv("LANGUAGE"="EN") seems to change the error message language immediately (tested using OSX). Where should I put this command for testthat? In the testthat.R file?
The R console is in German language, how can I set R to English?
Edit 3: As a first work-around I have put
Sys.setenv("LANGUAGE"="EN") # work-around to always create english R (error) messages
into my testthat.R file under the tests folder (it seems to work but I am not sure whether this is the right or best way...

Answer 1

Setting Sys.setenv("LANGUAGE" = "EN") works for me as well.
However, when testing with devtools::test() - as ctrl + shift + T in Rstudio will do - I had to call Sys.setenv() in the test scripts inside the tests/testthat/ directory. The reason being that devtools::test() will call testthat::test_dir() circumventing the tests/testthat.R file.
So far, this did not have undesirable side-effects. The environment variable will only be set for that particular R process as described in the help page:
Sys.setenv sets environment variables (for other processes called from within R or future calls to Sys.getenv from this R process).
For completeness, you can also unset the variable again on Windows (see comments).
Sys.setenv("LANGUAGE" = "DE")
expect_error(log("a"), "Nicht-numerisches Argument")
Sys.setenv("LANGUAGE" = "FR")
expect_error(log("a"), "argument non numérique ")
Sys.unsetenv("LANGUAGE")
RStudio might also give trouble (I was not able to change the language there interactively), but when executing with devtools::test() it works.
Finally, wrapping it in a helper function.
expect_error_lang <- function(..., lang = "EN") {
Sys.setenv("LANGUAGE" = lang)
expect_error(...)
Sys.unsetenv("LANGUAGE")
}
#...
expect_error_lang(log("a"), "non-numeric")
expect_error_lang(log("a"), "Nicht-numerisches", lang = "DE")
expect_error_lang(log("a"), "argument non", lang = "FR")