Creating Helper Function

Then you will be able to call it each time needed.

test_that("foofy() does this", {
  useful_thing1 <- new_useful_thing()
  expect_equal(foofy(useful_thing1, x = "this"), EXPECTED_FOOFY_OUTPUT)

test_that("foofy() does that", {
  useful_thing2 <- new_useful_thing()
  expect_equal(foofy(useful_thing2, x = "that"), EXPECTED_FOOFY_OUTPUT)

In many cases you might found out that the function can be useful even for creating vignettes and you might end exporting the function.