How to not run an example using roxygen2?

You can use \donttest{} to your example. The snippet will be provided in your documentation, but won't get tested with the R CMD Check.

For more info --> ?example

#' @example
\donttest{
    2^2
    }

This 2^2 won't get run when you run devtools::check()

---

EDIT

Per the latest release notes or NEWS for R 4.0.0, examples within \donttest{} will now be tested by default. This can, however, be overridden by setting environment variable _R_CHECK_DONTTEST_EXAMPLES_ to FALSE.

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.

According to this GitHub issues discussion (credited here), Hadley Wickham noted 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.

There are other ways as well that will let you continue to use donttest{}, refer the aforementioned discussions for the workarounds.

For those who are using @example path/to/example.R instead of the @examples tag you can use the \dontrun environment directly in the example.R file. For example

# example.R
\dontrun{
# this is a long running example
for(i in seq(1, 1e5)) { lm(mpg ~ wt, data = mtcars) }
}

# some other shorter example
2 + 2

Use \dontrun{}

#'@examples
#'\dontrun{
#'geocode("3817 Spruce St, Philadelphia, PA 19104")
#'geocode("Philadelphia, PA")
#'dat <- data.frame(value=runif(3),address=c("3817 Spruce St, Philadelphia, PA 19104","Philadelphia, PA","Neverneverland"))
#'geocode(dat)
#'}