Add extra test for custom property, use purrr::chuck()

use purrr::chuck() so we throw an error when the indexed object doesn't exist instead of passing the test

tests/testthat/test-write_package.R

@@ -336,14 +336,26 @@ test_that("write_package() encodes null and NA as null", {
       data = data.frame("col_1" = c(1, 2), "col_2" = c("a", "b")),
       title = NA
     )
-  expect_null(p$image)
-  expect_equal(p$resources[[4]]$title, NA)
+  # Set a custom property as NA, to see if it gets written as `null` in JSON
+  p$my_property <- NA
+
+  # Image is set as `NULL` in the JSON and that should still be the case here.
+  expect_null(purrr::chuck(p, "image"))
+
+  ## Use purrr::chuck() so an error is returned if image doesn't exist
+  expect_null(purrr::chuck(p, "image"))
+  expect_identical(p$resources[[4]]$title, NA)
+  expect_identical(p$my_property, NA)
 
   dir <- file.path(tempdir(), "package")
   on.exit(unlink(dir, recursive = TRUE))
   write_package(p, dir)
 
   p_loaded <- read_package(file.path(dir, "datapackage.json"))
-  expect_null(p_loaded$image)
-  expect_null(p_loaded$resources[[4]]$title)
+  # Use purrr::chuck() so an error is returned if the requested index doesn't
+  # exist
+  expect_null(purrr::chuck(p_loaded, "image"))
+  expect_null(purrr::chuck(p_loaded, "resources", 4, "title"))
+  ## my_property was set to NA, when writing this becomes NULL
+  expect_null(purrr::chuck(p_loaded, "my_property"))
 })