How to test that function correctly loads an image with magick::image_read()

Package development
1

Hello,

I am fairly new to writing tests and would love suggestions for how best to test a function that loads an image with the magick package.

I wrote a simple helper function for my R package to load an image with magick::image_read() with the input argument is the filepath for the image. I saved a test image

w0030_s03_pWOZ_r01

in my package as tests > testthat > fixtures > w0030_s03_pWOZ_r01.png.

Here's a minimal working example:

load_image <- function(image_path){
    if (file.exists(image_path)){
        return(magick::image_read(image_path))
    } else {
        stop("image_path does not exist.")
    }
}

Here are my attempts at writing tests for this function:

test_that("Load image works", {
    image_path <- testthat::test_path("fixtures", "w0030_s03_pWOZ_r01.png")
    actual <- load_image(image_path)
    expected <- magick::image_read(image_path)
    expect_identical(actual, expected)
    expect_s3_class(actual, "magick-image")
})

test_that("Load image fails if file does not exist", {
    image_path <- "fake.png"
    expect_error(load_image(image_path), "image_path does not exist.")
})

The tests "expect_s3_class(actual, "magick-image")" and "expect_error(load_image(image_path), "image_path does not exist.")" both pass but expect_identical(actual, expected) failed and gave the following message:

actual (actual) not identical to expected (expected).

actual is # A tibble: 1 × 7
expected is # A tibble: 1 × 7

actual is format width height colorspace matte filesize density
expected is format width height colorspace matte filesize density

actual is
expected is

actual is 1 PNG 548 125 Gray FALSE 23892 28x28
expected is 1 PNG 548 125 Gray FALSE 23892 28x28

Here are my questions:

  1. Any ideas why this test failed? What am I missing?
  2. Are there different tests I should be running on this function?

Thank you for your help!
Stephanie