test_that desc with line breaks causes expect_snapshot to always be overwritten.

[LDSamson]

Perhaps good to know that long descriptions in testthat::describe() or testthat::test_that(), as for example here, cause issues with testthat::expect_snapshot() for me. See the issue that I opened here.

[mjfrigaard]

Thank you for pointing this out! I will make a note of this in test tools.

BTW I started building this tiny package of BDD helpers that seems to be working (so far). I'll test it with snapshots 😃

[LDSamson]

Note that I think it only occurs when there are line breaks in the description. Code like this still works, as far as I tested:

test_that(
  paste0(
    "A long description", 
    "over multiple lines"
  ), {
    expect_snapshot(2*4)
  }
)

[mjfrigaard]

I added a warning in test tools and included a shoutout 😃 . If you wrap the call to test_that() in a describe() it works:

describe(
    "Scenario: 
    Given 
    When 
    Then ",
    code = {
    test_that("fun()", code = {
      expect_snapshot(fun())
    })
  })

[LDSamson]

Thank you for the shout out! Glad that the feedback was useful. Strange that it works when test_that() is wrapped inside describe(), since if you replace the test_that() with testthat::it() the problem occurs again. This would be a good workaround for now indeed, nice.

[LDSamson]

Short update, since I checked the source code of expect_snapshot() (although you probably already noticed this):
the reason why this works:

describe(
  "Long
  description", 
  {
    test_that("test me", {expect_snapshot(2*2)})
  }
)

is because test_that() does not look for the description in describe() and will not add this description to the snapshot, while the function it() does . The problem is purely with the line breaks in the snapshot descriptions that are converted to \n characters.

I wrote a small pull request for the testthat package that should resolve the issue. Lets wait and see if the Posit team likes the solution!

[LDSamson]

@mjfrigaard I saw that the small fix I proposed in testthat is approved and merged, so this problem should now be resolved in the latest testthat version! (version 3.2.2) https://github.com/r-lib/testthat/blob/main/NEWS.md r-lib/testthat#1902