I submitted a package to CRAN and they asked me to replace \dontrun{} by \donttest{} in the Rd-files and resubmit. I was using \dontrun{} to wrap some examples that are supposed to throw error messages.
After replacing \dontrun{} by \donttest{} I conducted some tests and R CMD check still succeeds but it happens that now both devtools::check() and R CMD check --as-cran fail due to the examples wrapped in \donttest{}:
checking examples with --run-donttest ... ERROR
After some browsing I learned that R 4.0.0 has changed R CMD check --as-cran to run \donttest examples. According to the NEWS of R-devel:
"R CMD check --as-cran now runs \donttest examples (which are run by example()) instead of instructing the tester to do so. This can be temporarily circumvented during development by setting environment variable R_CHECK_DONTTEST_EXAMPLES to a false value."
Since I intend to resubmit the package to CRAN, setting _R_CHECK_DONTTEST_EXAMPLES_ to false locally will not help me.
I also found this recent discussion in a devtools issue where Hadley Wickham states that:
"Generally, now if you don't want to run tests on CRAN \dontrun{} is more likely to work, but using \dontrun{} may cause initial submission to fail."
So now I don't know how to proceed because if I resubmit the package with the required changes I already know it will throw an error in R CMD check --as-cran, and hence it will probably fail CRAN's automatic pretests.
EDIT:
As suggested here I tried if(interactive()){} instead of \dontrun{}. This solution succeeds in R CMD check --as-cran and devtools::check() but I don't think it is the most appropriate way to address this problem since it does not work well with example() (throws an error and does not show the remaining examples). \dontrun{} works better with example() as it prints all the examples but comments out the ones wrapped with \dontrun{}.
If you know that something will throw an error, you can wrap it in try().
## example of failing code
try(stop("Here is an error"))