tests/testthat/test-image-diff.R

In rstudio/shinytest2: Testing for Shiny Applications

img_folder <- system.file("example/imgs", package = "shinytest2")
bookmark_new <- fs::path(img_folder, "bookmark-new.png")
bookmark_old <- fs::path(img_folder, "bookmark-old.png")

slider_new <- fs::path(img_folder, "slider-new.png")
slider_old <- fs::path(img_folder, "slider-old.png")

test_that("screenshot options are used", {
  skip_if_not_installed("png")

  expect_false(
    compare_screenshot_threshold(
      bookmark_old,
      bookmark_new,
    )
  )

  withr::with_options(
    list("shinytest2.compare_screenshot.threshold" = 1),
    {
      # Slightly different images
      expect_true(
        compare_screenshot_threshold(
          bookmark_old,
          bookmark_new,
        )
      )
    }
  )

  small_max_diff <-
    screenshot_max_difference(
      slider_old,
      slider_new,
      kernel_size = 5
    )

  withr::with_options(
    list("shinytest2.compare_screenshot.kernel_size" = 10),
    {
      big_max_diff <-
        screenshot_max_difference(
          slider_old,
          slider_new,
        )
    }
  )
  print(list(small_max_diff, big_max_diff))
  expect_lt(small_max_diff, big_max_diff)
})

test_that("convolution can be performed", {
  skip_if_not_installed("png")
  # Using `brew install graphicsmagick`
  # `gm compare 151-original-linux-3_6-79bf3a4.png 151-new-linux-3_6-446865a.png -highlight-style assign -file 151-diff.png`
  # `gm compare bers3-1.png bers3-2.png -highlight-style assign -file bers3-diff.png`

  # Same image
  expect_true(
    compare_screenshot_threshold(
      bookmark_old,
      bookmark_old,
      threshold = NULL
    )
  )
  # Same image
  expect_true(
    compare_screenshot_threshold(
      bookmark_old,
      bookmark_old,
      threshold = 0
    )
  )

  # Slightly different images
  expect_true(
    compare_screenshot_threshold(
      bookmark_old,
      bookmark_new,
      threshold = 1
    )
  )


  # Slightly different images
  expect_false(
    compare_screenshot_threshold(
      slider_old,
      slider_new,
      threshold = 28.1,
      quiet = TRUE
    )
  )

  expect_silent({
    ans <-
      compare_screenshot_threshold(
        slider_old,
        slider_new,
        threshold = 28.2
      )
  })
  expect_true(ans, label = "compare_screenshot_threshold(slider_old, slider_new, threshold = 28.2)")
})


test_that("kernel size makes a difference", {
  skip_if_not_installed("png")

  small_max_diff <-
    screenshot_max_difference(
      slider_old,
      slider_new,
      kernel_size = 5
    )
  big_max_diff <-
    screenshot_max_difference(
      slider_old,
      slider_new,
      kernel_size = 10
    )

  expect_lt(small_max_diff, big_max_diff)
  expect_gt(small_max_diff, 0)
  expect_gt(big_max_diff, 44)
  expect_lt(big_max_diff, 50)
})


test_that("Errors in screenshot_max_difference do not cause errors in compare_screenshot_threshold", {
  expect_silent({
    comp_val <-
      compare_screenshot_threshold(
        slider_old,
        bookmark_old,
        threshold = 5
      )
  })
  expect_false(comp_val)

})