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HTTP testing in R

31 Gotchas

There’s a few things to watch out for when using vcr.

  • Security: Don’t put your secure API keys, tokens, etc. on the public web. See the Security chapter and the vcr security chapter.
  • API key issues: Running vcr enabled tests in different contexts when API keys are used can have some rough edges.
  • Dates: Be careful when using dates in tests with vcr. e.g. if you generate todays date, and pass that in to a function in your package that uses that date for an HTTP request, the date will be different from the one in the matching cassette, causing a vcr failure.
  • HTTP errors: It’s a good idea to test failure behavior of a web service in your test suite. Sometimes vcr can handle that and sometimes it cannot. Open any issues about this because ideally i think vcr could handle all cases of HTTP failures.
  • Very large response bodies: A few things about large response bodies. First, vcr may give you trouble with very large response bodies as we’ve see yaml parsing problems already. Second, large response bodies means large cassettes on disk - so just be aware of the file size if that’s something that matters to you. Third, large response bodies will take longer to load into R, so you may still have a multi second test run even though the test is using a cached HTTP response.
  • Encoding: We haven’t dealt with encoding much yet at all, so we’re likely to run into encoding issues. One blunt instrument for this for now is to set preserve_exact_body_bytes = TRUE when running vcr::use_cassette() or vcr::insert_cassette(), which stores the response body as base64.
  • devtools::check vs. devtools::test: See (22.5.1)
  • ignored files: See (30)

31.1 Correct line identification

To get the actual lines where failures occur, you can wrap the test_that block in a use_cassette() block:

library(testthat)
vcr::use_cassette("rl_citation", {
  test_that("my test", {
    aa <- rl_citation()

    expect_is(aa, "character")
    expect_match(aa, "IUCN")
    expect_match(aa, "www.iucnredlist.org")
  })
})

OR put the use_cassette() block on the inside, but make sure to put testthat expectations outside of the use_cassette() block:

library(testthat)
test_that("my test", {
  vcr::use_cassette("rl_citation", {
    aa <- rl_citation()
  })

  expect_is(aa, "character")
  expect_match(aa, "IUCN")
  expect_match(aa, "www.iucnredlist.org")
})

Do not wrap the use_cassette() block inside your test_that() block with testthat expectations inside the use_cassette() block, as you’ll only get the line number that the use_cassette() block starts on on failures.