testthat: handling both warning and value

Question

What's the best way to handle calls that generate a warning but then also return a value?

e.g.

> require(testthat)
> expect_warning(log(-1))
> expect_equal(log(-1), NaN)
Warning message:
In log(-1) : NaNs produced

I want to write the test such that the call to log(-1) should both (a) generate a warning and (b) return the value NaN. The way above works, but seeing the "Warning message:" at the bottom might confuse people. Should I suppress warnings temporarily?

Answer 1

require(testthat)
expect_warning(val <- log(-1))
expect_true(is.nan(val))

Answer 2

One great way to deal with value, message and warning is to use the adverb purrr::quietly like that:

## R/foo.r
foo <- function() {
  message("This is a message")
  warning("This is a warning")
  "This is a result"
}

test_that("foo works", {
  qfoo <- purrr::quietly(foo)
  qfoo_call <- qfoo()
  expect_equal(qfoo_call$result, "This is a result")
  expect_equal(qfoo_call$message, "This is a message")
  expect_equal(qfoo_call$warning, "This is a warning")
})

---

See this question to see all the benefits of this approach.