Run a single test function in R's testthat

Question

R's testthat package has a number of functions for running tests: https://testthat.r-lib.org/reference/index.html#run-tests. However, the most coarse level you can filter tests seems to be at a file level, since there is a test_file() function that doesn't have any filtering arguments, and test_dir() has a filter argument but it is only used to filter by filename.

However I frequently want to only run a single test, because it's new, or because I know it's relevant to a change I just made.

Is there a way, in the R console or in RStudio to run a single testthat test? If not, is there some other recommended solution to this problem such as putting each test in it's own file (this seems pretty painful though)?

Answer 1

As of testthat version 3.2.0 CRAN release: 2023-10-06:

test_file() gains a desc argument which allows you to run a single test from a file.

For example, if you have a test file (test-mytest.R) containing tests for two functions (consider these simple functions converting temperature):

test_that(desc = "Fahrenheit to Celsius", code = {

  temp_C <- F_to_C(50)

  expect_equal(object = temp_C, expected = 10)
  expect_type(object = temp_C, type = "double")
})

test_that(desc = "Celsius to Fahrenheit", code = {

  temp_F <- C_to_F(100)

  expect_equal(object = temp_F, expected = 212)
  expect_type(object = temp_F, type = "double")
})

If you want to run all tests in the file:

R> test_file("tests/testthat/test-mytest.R")
[ FAIL 0 | WARN 0 | SKIP 0 | PASS 4 ]

If you want a single test, use the optional desc argument to indicate the test name:

R> test_file("tests/testthat/test-mytest.R", desc = "Fahrenheit to Celsius")
[ FAIL 0 | WARN 0 | SKIP 0 | PASS 2 ]