diff --git a/R/add_files.R b/R/add_files.R
index 663cdd2d..bdd0f9e1 100644
--- a/R/add_files.R
+++ b/R/add_files.R
@@ -44,7 +44,7 @@ add_js_file <- function(
     msg = "`name` is required"
   )
 
-  check_name_length(name)
+  check_name_length_is_one(name)
 
   name <- file_path_sans_ext(name)
 
@@ -112,7 +112,7 @@ add_js_handler <- function(
     msg = "`name` is required"
   )
 
-  check_name_length(name)
+  check_name_length_is_one(name)
 
   name <- file_path_sans_ext(name)
 
@@ -177,7 +177,7 @@ add_js_input_binding <- function(
     msg = "`name` is required"
   )
 
-  check_name_length(name)
+  check_name_length_is_one(name)
 
   attempt::stop_if(
     length(events$name) == 0,
@@ -319,7 +319,7 @@ add_js_output_binding <- function(
     msg = "`name` is required"
   )
 
-  check_name_length(name)
+  check_name_length_is_one(name)
 
   raw_name <- name
 
@@ -403,7 +403,7 @@ add_css_file <- function(
     msg = "`name` is required"
   )
 
-  check_name_length(name)
+  check_name_length_is_one(name)
 
   name <- file_path_sans_ext(name)
 
@@ -465,7 +465,7 @@ add_sass_file <- function(
     msg = "`name` is required"
   )
 
-  check_name_length(name)
+  check_name_length_is_one(name)
 
   name <- file_path_sans_ext(name)
 
@@ -532,7 +532,7 @@ add_html_template <- function(
 ) {
   name <- file_path_sans_ext(name)
 
-  check_name_length(name)
+  check_name_length_is_one(name)
 
   old <- setwd(fs_path_abs(pkg))
   on.exit(setwd(old))
@@ -601,7 +601,7 @@ add_partial_html_template <- function(
   dir_create = TRUE
 ) {
   name <- file_path_sans_ext(name)
-  check_name_length(name)
+  check_name_length_is_one(name)
 
   old <- setwd(fs_path_abs(pkg))
   on.exit(setwd(old))
diff --git a/R/add_r_files.R b/R/add_r_files.R
index eb8a42af..881642b4 100644
--- a/R/add_r_files.R
+++ b/R/add_r_files.R
@@ -9,7 +9,7 @@ add_r_files <- function(
 ) {
   name <- file_path_sans_ext(name)
 
-  check_name_length(name)
+  check_name_length_is_one(name)
 
   old <- setwd(fs_path_abs(pkg))
   on.exit(setwd(old))
diff --git a/R/modules_fn.R b/R/modules_fn.R
index 13b3293b..c2b6b336 100644
--- a/R/modules_fn.R
+++ b/R/modules_fn.R
@@ -39,7 +39,7 @@ add_module <- function(
   ...
     ) {
   # Let's start with the checks for the validity of the name
-  check_name_length(name)
+  check_name_length_is_one(name)
   check_name_syntax(name)
 
   # We now check that:
diff --git a/R/use_files.R b/R/use_files.R
index 1c322f5d..94df6d19 100644
--- a/R/use_files.R
+++ b/R/use_files.R
@@ -18,12 +18,12 @@
 #' @return The path to the file, invisibly.
 use_external_js_file <- function(
   url,
-  name,
+  name = NULL,
   pkg = get_golem_wd(),
   dir = "inst/app/www",
   open = FALSE,
   dir_create = TRUE
-) {
+    ) {
   old <- setwd(fs_path_abs(pkg))
   on.exit(setwd(old))
 
@@ -31,17 +31,24 @@ use_external_js_file <- function(
     name <- basename(url)
   }
 
-  check_name_length(name)
+  check_name_length_is_one(name)
 
   name <- file_path_sans_ext(name)
   new_file <- sprintf("%s.js", name)
 
-  dir_created <- create_if_needed(
-    dir,
-    type = "directory"
+  dir_created <- tryCatch(
+    create_if_needed(
+      dir,
+      type = "directory"
+    ),
+    error = function(e) {
+      out <- FALSE
+      names(out) <- e[[1]]
+      return(out)
+    }
   )
 
-  if (!dir_created) {
+  if (isFALSE(dir_created)) {
     cat_dir_necessary()
     return(invisible(FALSE))
   }
@@ -85,12 +92,12 @@ use_external_js_file <- function(
 #' @rdname use_files
 use_external_css_file <- function(
   url,
-  name,
+  name = NULL,
   pkg = get_golem_wd(),
   dir = "inst/app/www",
   open = FALSE,
   dir_create = TRUE
-) {
+    ) {
   old <- setwd(fs_path_abs(pkg))
   on.exit(setwd(old))
 
@@ -98,17 +105,24 @@ use_external_css_file <- function(
     name <- basename(url)
   }
 
-  check_name_length(name)
+  check_name_length_is_one(name)
 
   name <- file_path_sans_ext(name)
   new_file <- sprintf("%s.css", name)
 
-  dir_created <- create_if_needed(
-    dir,
-    type = "directory"
+  dir_created <- tryCatch(
+    create_if_needed(
+      dir,
+      type = "directory"
+    ),
+    error = function(e) {
+      out <- FALSE
+      names(out) <- e[[1]]
+      return(out)
+    }
   )
 
-  if (!dir_created) {
+  if (isFALSE(dir_created)) {
     cat_dir_necessary()
     return(invisible(FALSE))
   }
@@ -157,7 +171,7 @@ use_external_html_template <- function(
   dir = "inst/app/www",
   open = FALSE,
   dir_create = TRUE
-) {
+    ) {
   old <- setwd(fs_path_abs(pkg))
   on.exit(setwd(old))
 
@@ -166,14 +180,21 @@ use_external_html_template <- function(
     file_path_sans_ext(name)
   )
 
-  check_name_length(name)
-
-  dir_created <- create_if_needed(
-    dir,
-    type = "directory"
+  check_name_length_is_one(name)
+
+  dir_created <- tryCatch(
+    create_if_needed(
+      dir,
+      type = "directory"
+    ),
+    error = function(e) {
+      out <- FALSE
+      names(out) <- e[[1]]
+      return(out)
+    }
   )
 
-  if (!dir_created) {
+  if (isFALSE(dir_created)) {
     cat_dir_necessary()
     return(invisible(FALSE))
   }
@@ -211,28 +232,34 @@ use_external_html_template <- function(
 #' @rdname use_files
 use_external_file <- function(
   url,
-  name,
+  name = NULL,
   pkg = get_golem_wd(),
   dir = "inst/app/www",
   open = FALSE,
   dir_create = TRUE
-) {
-  check_name_length(name)
-
+    ) {
   if (missing(name)) {
     name <- basename(url)
   }
 
+  check_name_length_is_one(name)
 
   old <- setwd(fs_path_abs(pkg))
   on.exit(setwd(old))
 
-  dir_created <- create_if_needed(
-    dir,
-    type = "directory"
+  dir_created <- tryCatch(
+    create_if_needed(
+      dir,
+      type = "directory"
+    ),
+    error = function(e) {
+      out <- FALSE
+      names(out) <- e[[1]]
+      return(out)
+    }
   )
 
-  if (!dir_created) {
+  if (isFALSE(dir_created)) {
     cat_dir_necessary()
     return(invisible(FALSE))
   }
@@ -260,13 +287,12 @@ use_external_file <- function(
 #' @rdname use_files
 use_internal_js_file <- function(
   path,
-  name,
+  name = NULL,
   pkg = get_golem_wd(),
   dir = "inst/app/www",
   open = FALSE,
   dir_create = TRUE
-) {
-  check_name_length(name)
+    ) {
   old <- setwd(fs_path_abs(pkg))
   on.exit(setwd(old))
 
@@ -274,15 +300,24 @@ use_internal_js_file <- function(
     name <- basename(path)
   }
 
+  check_name_length_is_one(name)
+
   name <- file_path_sans_ext(name)
   new_file <- sprintf("%s.js", name)
 
-  dir_created <- create_if_needed(
-    dir,
-    type = "directory"
+  dir_created <- tryCatch(
+    create_if_needed(
+      dir,
+      type = "directory"
+    ),
+    error = function(e) {
+      out <- FALSE
+      names(out) <- e[[1]]
+      return(out)
+    }
   )
 
-  if (!dir_created) {
+  if (isFALSE(dir_created)) {
     cat_dir_necessary()
     return(invisible(FALSE))
   }
@@ -325,14 +360,12 @@ use_internal_js_file <- function(
 #' @rdname use_files
 use_internal_css_file <- function(
   path,
-  name,
+  name = NULL,
   pkg = get_golem_wd(),
   dir = "inst/app/www",
   open = FALSE,
   dir_create = TRUE
-) {
-  check_name_length(name)
-
+    ) {
   old <- setwd(fs_path_abs(pkg))
   on.exit(setwd(old))
 
@@ -340,15 +373,24 @@ use_internal_css_file <- function(
     name <- basename(path)
   }
 
+  check_name_length_is_one(name)
+
   name <- file_path_sans_ext(name)
   new_file <- sprintf("%s.css", name)
 
-  dir_created <- create_if_needed(
-    dir,
-    type = "directory"
+  dir_created <- tryCatch(
+    create_if_needed(
+      dir,
+      type = "directory"
+    ),
+    error = function(e) {
+      out <- FALSE
+      names(out) <- e[[1]]
+      return(out)
+    }
   )
 
-  if (!dir_created) {
+  if (isFALSE(dir_created)) {
     cat_dir_necessary()
     return(invisible(FALSE))
   }
@@ -396,23 +438,30 @@ use_internal_html_template <- function(
   dir = "inst/app/www",
   open = FALSE,
   dir_create = TRUE
-) {
+    ) {
   old <- setwd(fs_path_abs(pkg))
   on.exit(setwd(old))
 
-  check_name_length(name)
+  check_name_length_is_one(name)
 
   new_file <- sprintf(
     "%s.html",
     file_path_sans_ext(name)
   )
 
-  dir_created <- create_if_needed(
-    dir,
-    type = "directory"
+  dir_created <- tryCatch(
+    create_if_needed(
+      dir,
+      type = "directory"
+    ),
+    error = function(e) {
+      out <- FALSE
+      names(out) <- e[[1]]
+      return(out)
+    }
   )
 
-  if (!dir_created) {
+  if (isFALSE(dir_created)) {
     cat_dir_necessary()
     return(invisible(FALSE))
   }
@@ -449,27 +498,34 @@ use_internal_html_template <- function(
 #' @rdname use_files
 use_internal_file <- function(
   path,
-  name,
+  name = NULL,
   pkg = get_golem_wd(),
   dir = "inst/app/www",
   open = FALSE,
   dir_create = TRUE
-) {
+    ) {
   if (missing(name)) {
     name <- basename(path)
   }
 
-  check_name_length(name)
+  check_name_length_is_one(name)
 
   old <- setwd(fs_path_abs(pkg))
   on.exit(setwd(old))
 
-  dir_created <- create_if_needed(
-    dir,
-    type = "directory"
+  dir_created <- tryCatch(
+    create_if_needed(
+      dir,
+      type = "directory"
+    ),
+    error = function(e) {
+      out <- FALSE
+      names(out) <- e[[1]]
+      return(out)
+    }
   )
 
-  if (!dir_created) {
+  if (isFALSE(dir_created)) {
     cat_dir_necessary()
     return(invisible(FALSE))
   }
diff --git a/R/utils.R b/R/utils.R
index 31edfb6f..71586c8e 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -477,7 +477,7 @@ is_existing_module <- function(module) {
 # This function is used for checking
 # that  the name argument of the function
 # creating files is not of length() > 1
-check_name_length <- function(name) {
+check_name_length_is_one <- function(name) {
   stop_if(
     name,
     ~ length(.x) > 1,
diff --git a/README.md b/README.md
index c654d477..f131b398 100644
--- a/README.md
+++ b/README.md
@@ -112,7 +112,7 @@ This `README` has been compiled on the
 
 ``` r
 Sys.time()
-#> [1] "2023-08-08 14:20:03 UTC"
+#> [1] "2023-08-08 18:26:15 UTC"
 ```
 
 Here are the test & coverage results:
@@ -121,21 +121,20 @@ Here are the test & coverage results:
 devtools::check(quiet = TRUE)
 #> ℹ Loading golem
 #> ── R CMD check results ─────────────────────────────────────── golem 0.4.12 ────
-#> Duration: 2m 36.7s
+#> Duration: 2m 36.2s
 #> 
 #> 0 errors ✔ | 0 warnings ✔ | 0 notes ✔
 ```
 
 ``` r
 covr::package_coverage()
-#> golem Coverage: 75.69%
+#> golem Coverage: 84.32%
 #> R/addins.R: 0.00%
 #> R/bootstrap_rstudio_api.R: 0.00%
 #> R/enable_roxygenize.R: 0.00%
 #> R/get_sysreqs.R: 0.00%
 #> R/run_dev.R: 0.00%
 #> R/sanity_check.R: 0.00%
-#> R/use_files.R: 0.00%
 #> R/test_helpers.R: 30.26%
 #> R/js.R: 43.75%
 #> R/reload.R: 45.36%
@@ -149,7 +148,7 @@ covr::package_coverage()
 #> R/modules_fn.R: 79.00%
 #> R/golem-yaml-set.R: 83.02%
 #> R/use_utils.R: 83.33%
-#> R/utils.R: 85.13%
+#> R/utils.R: 85.50%
 #> R/add_rstudio_files.R: 88.52%
 #> R/add_resource_path.R: 88.89%
 #> R/create_golem.R: 89.47%
@@ -177,6 +176,7 @@ covr::package_coverage()
 #> R/pkg_tools.R: 100.00%
 #> R/set_golem_options.R: 100.00%
 #> R/templates.R: 100.00%
+#> R/use_files.R: 100.00%
 #> R/with_opt.R: 100.00%
 ```
 
diff --git a/inst/utils/testfile_template_css.css b/inst/utils/testfile_template_css.css
new file mode 100644
index 00000000..2beaf256
--- /dev/null
+++ b/inst/utils/testfile_template_css.css
@@ -0,0 +1,13 @@
+ body {
+  background-color: lightblue;
+}
+
+h1 {
+  color: white;
+  text-align: center;
+}
+
+p {
+  font-family: verdana;
+  font-size: 20px;
+}
diff --git a/inst/utils/testfile_template_html.html b/inst/utils/testfile_template_html.html
new file mode 100644
index 00000000..c87692f8
--- /dev/null
+++ b/inst/utils/testfile_template_html.html
@@ -0,0 +1,10 @@
+<!DOCTYPE html>
+<html>
+<body>
+
+<h1>My First Heading</h1>
+
+<p>My first paragraph.</p>
+
+</body>
+</html>
diff --git a/inst/utils/testfile_template_js.js b/inst/utils/testfile_template_js.js
new file mode 100644
index 00000000..e282ac1d
--- /dev/null
+++ b/inst/utils/testfile_template_js.js
@@ -0,0 +1,2 @@
+const myHeading = document.querySelector("h1");
+myHeading.textContent = "Hello world!";
diff --git a/inst/utils/testfile_template_plainfile.txt b/inst/utils/testfile_template_plainfile.txt
new file mode 100644
index 00000000..3e715502
--- /dev/null
+++ b/inst/utils/testfile_template_plainfile.txt
@@ -0,0 +1 @@
+Some text.
diff --git a/man/use_files.Rd b/man/use_files.Rd
index 6fabee36..81ca47ca 100644
--- a/man/use_files.Rd
+++ b/man/use_files.Rd
@@ -13,7 +13,7 @@
 \usage{
 use_external_js_file(
   url,
-  name,
+  name = NULL,
   pkg = get_golem_wd(),
   dir = "inst/app/www",
   open = FALSE,
@@ -22,7 +22,7 @@ use_external_js_file(
 
 use_external_css_file(
   url,
-  name,
+  name = NULL,
   pkg = get_golem_wd(),
   dir = "inst/app/www",
   open = FALSE,
@@ -40,7 +40,7 @@ use_external_html_template(
 
 use_external_file(
   url,
-  name,
+  name = NULL,
   pkg = get_golem_wd(),
   dir = "inst/app/www",
   open = FALSE,
@@ -49,7 +49,7 @@ use_external_file(
 
 use_internal_js_file(
   path,
-  name,
+  name = NULL,
   pkg = get_golem_wd(),
   dir = "inst/app/www",
   open = FALSE,
@@ -58,7 +58,7 @@ use_internal_js_file(
 
 use_internal_css_file(
   path,
-  name,
+  name = NULL,
   pkg = get_golem_wd(),
   dir = "inst/app/www",
   open = FALSE,
@@ -76,7 +76,7 @@ use_internal_html_template(
 
 use_internal_file(
   path,
-  name,
+  name = NULL,
   pkg = get_golem_wd(),
   dir = "inst/app/www",
   open = FALSE,
diff --git a/tests/testthat/test-add_files.R b/tests/testthat/test-add_files.R
index ba8762e2..8c3d2490 100644
--- a/tests/testthat/test-add_files.R
+++ b/tests/testthat/test-add_files.R
@@ -10,7 +10,7 @@ expect_add_file <- function(
   # Be sure to remove all files in case there are
   remove_files("inst/app/www", ext)
 
-  # Checking that check_name_length is throwing an error
+  # Checking that check_name_length_is_one is throwing an error
   expect_error(
     fun(c("a", "b")),
   )
diff --git a/tests/testthat/test-use_files.R b/tests/testthat/test-use_files.R
new file mode 100644
index 00000000..23aece6b
--- /dev/null
+++ b/tests/testthat/test-use_files.R
@@ -0,0 +1,410 @@
+test_that("use_external_XXX_files() function family works properly", {
+  path_dummy_golem <- tempfile(pattern = "dummygolem")
+  create_golem(
+    path = path_dummy_golem,
+    open = FALSE
+  )
+  with_dir(
+    path_dummy_golem,
+    {
+      # I. test the external ".txt" file download
+      # I.A standard case
+      use_external_file(
+        url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_plainfile.txt"
+      )
+      test_file_download <- readLines(
+        "inst/app/www/testfile_template_plainfile.txt"
+      )
+      expect_identical(
+        test_file_download,
+        "Some text."
+      )
+      # I.B corner case: file already exists
+      expect_false(
+        use_external_file(
+          url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_plainfile.txt",
+          name = "testfile_template_plainfile.txt"
+        )
+      )
+      # I.C corner case: dir already exists
+      expect_false(
+        use_external_file(
+          url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_plainfile.txt",
+          name = "testfile_template_plainfile3.txt",
+          dir = "inst/app/www2"
+        )
+      )
+
+      # II. test the external ".html" file download
+      # II.A standard case
+      use_external_html_template(
+        url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_html.html",
+        name = "testfile_template_html.html"
+      )
+      test_file_download <- readLines(
+        "inst/app/www/testfile_template_html.html"
+      )
+      expect_identical(
+        test_file_download,
+        c(
+          "<!DOCTYPE html>",
+          "<html>",
+          "<body>",
+          "",
+          "<h1>My First Heading</h1>",
+          "",
+          "<p>My first paragraph.</p>",
+          "",
+          "</body>",
+          "</html>"
+        )
+      )
+      # II.B corner case: file already exists
+      expect_false(
+        use_external_html_template(
+          url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_html.html",
+          name = "testfile_template_html.html"
+        )
+      )
+      # II.C corner case: dir already exists
+      expect_false(
+        use_external_html_template(
+          url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_html.html",
+          name = "testfile_template_html2.html",
+          dir = "inst/app/www2"
+        )
+      )
+
+      # III. test the external ".js" file download
+      # III.A standard case
+      use_external_js_file(
+        url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_js.js"
+      )
+      test_file_download <- readLines(
+        "inst/app/www/testfile_template_js.js"
+      )
+      expect_identical(
+        test_file_download,
+        c(
+          "const myHeading = document.querySelector(\"h1\");",
+          "myHeading.textContent = \"Hello world!\";"
+        )
+      )
+      # III.B corner case: file already exists
+      expect_false(
+        use_external_js_file(
+          url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_js.js",
+          name = "testfile_template_js.js"
+        )
+      )
+      # III.C corner case: dir already exists
+      expect_false(
+        use_external_js_file(
+          url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_js.js",
+          name = "testfile_template_js2.js",
+          dir = "inst/app/www2"
+        )
+      )
+      # III.D corner case: URL does not have extension ".js"
+      expect_false(
+        use_external_js_file(
+          url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_js",
+          name = "testfile_template_js3.js"
+        )
+      )
+
+      # IV. test the external ".css" file download
+      # IV.A standard case
+      use_external_css_file(
+        url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_css.css"
+      )
+      test_file_download <- readLines(
+        "inst/app/www/testfile_template_css.css"
+      )
+      expect_identical(
+        test_file_download,
+        c(
+          " body {",
+          "  background-color: lightblue;",
+          "}",
+          "",
+          "h1 {",
+          "  color: white;",
+          "  text-align: center;",
+          "}",
+          "",
+          "p {",
+          "  font-family: verdana;",
+          "  font-size: 20px;",
+          "}"
+        )
+      )
+      # IV.B corner case: file already exists
+      expect_false(
+        use_external_css_file(
+          url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_css.css",
+          name = "testfile_template_css.css"
+        )
+      )
+      # IV.C corner case: dir already exists
+      expect_false(
+        use_external_css_file(
+          url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_css.css",
+          name = "testfile_template_css2.css",
+          dir = "inst/app/www2"
+        )
+      )
+      # IV.D corner case: URL does not have extension ".css"
+      expect_false(
+        use_external_css_file(
+          url = "https://raw.githubusercontent.com/ThinkR-open/golem/dev/inst/utils/testfile_template_css",
+          name = "testfile_template_css3.css"
+        )
+      )
+
+      unlink(path_dummy_golem, recursive = TRUE)
+    }
+  )
+})
+test_that("use_internal_XXX_files() function family works properly", {
+  path_dummy_golem <- tempfile(pattern = "dummygolem")
+  create_golem(
+    path = path_dummy_golem,
+    open = FALSE
+  )
+  dir.create(file.path(path_dummy_golem, "tmp_dump_testfiles"))
+  file.copy(
+    from = file.path(
+      .libPaths()[1],
+      "golem",
+      "utils",
+      c(
+        "testfile_template_plainfile.txt",
+        "testfile_template_html.html",
+        "testfile_template_js.js",
+        "testfile_template_css.css"
+      )
+    ),
+    to = file.path(
+      path_dummy_golem,
+      "tmp_dump_testfiles"
+    )
+  )
+  with_dir(
+    path_dummy_golem,
+    {
+      # I. test the internal ".txt" file usage
+      # I.A standard case
+      use_internal_file(
+        path = file.path(
+          path_dummy_golem,
+          "tmp_dump_testfiles",
+          "testfile_template_plainfile.txt"
+        )
+      )
+      test_file_download <- readLines(
+        "inst/app/www/testfile_template_plainfile.txt"
+      )
+      expect_identical(
+        test_file_download,
+        "Some text."
+      )
+      # I.B corner case: file already exists
+      expect_false(
+        use_internal_file(
+          path = file.path(
+            path_dummy_golem,
+            "tmp_dump_testfiles",
+            "testfile_template_plainfile.txt"
+          ),
+          name = "testfile_template_plainfile.txt"
+        )
+      )
+      # I.C corner case: dir already exists
+      expect_false(
+        use_internal_file(
+          path = file.path(
+            path_dummy_golem,
+            "tmp_dump_testfiles",
+            "testfile_template_plainfile.txt"
+          ),
+          name = "testfile_template_plainfile2.txt",
+          dir = "inst/app/www2"
+        )
+      )
+
+      # II. test the internal ".html" file usage
+      # II.A standard case
+      use_internal_html_template(
+        path = file.path(
+          path_dummy_golem,
+          "tmp_dump_testfiles",
+          "testfile_template_html.html"
+        ),
+        name = "testfile_template_html.html"
+      )
+      test_file_download <- readLines(
+        "inst/app/www/testfile_template_html.html"
+      )
+      expect_identical(
+        test_file_download,
+        c(
+          "<!DOCTYPE html>",
+          "<html>",
+          "<body>",
+          "",
+          "<h1>My First Heading</h1>",
+          "",
+          "<p>My first paragraph.</p>",
+          "",
+          "</body>",
+          "</html>"
+        )
+      )
+      # II.B corner case: file already exists
+      expect_false(
+        use_internal_html_template(
+          path = file.path(
+            path_dummy_golem,
+            "tmp_dump_testfiles",
+            "testfile_template_html.html"
+          ),
+          name = "testfile_template_html.html"
+        )
+      )
+      # II.C corner case: dir already exists
+      expect_false(
+        use_internal_html_template(
+          path = file.path(
+            path_dummy_golem,
+            "tmp_dump_testfiles",
+            "testfile_template_html.html"
+          ),
+          name = "testfile_template_html2.html",
+          dir = "inst/app/www2"
+        )
+      )
+
+      # III. test the internal ".js" file usage
+      # III.A standard case
+      use_internal_js_file(
+        path = file.path(
+          path_dummy_golem,
+          "tmp_dump_testfiles",
+          "testfile_template_js.js"
+        )
+      )
+      test_file_download <- readLines(
+        "inst/app/www/testfile_template_js.js"
+      )
+      expect_identical(
+        test_file_download,
+        c(
+          "const myHeading = document.querySelector(\"h1\");",
+          "myHeading.textContent = \"Hello world!\";"
+        )
+      )
+      # III.B corner case: file already exists
+      expect_false(
+        use_internal_js_file(
+          path = file.path(
+            path_dummy_golem,
+            "tmp_dump_testfiles",
+            "testfile_template_js.js"
+          ),
+          name = "testfile_template_js.js"
+        )
+      )
+      # III.C corner case: dir already exists
+      expect_false(
+        use_internal_js_file(
+          path = file.path(
+            path_dummy_golem,
+            "tmp_dump_testfiles",
+            "testfile_template_js2.js"
+          ),
+          name = "testfile_template_js.js",
+          dir = "inst/app/www2"
+        )
+      )
+      # III.D corner case: file path does not have extension ".js"
+      expect_false(
+        use_internal_js_file(
+          path = file.path(
+            path_dummy_golem,
+            "tmp_dump_testfiles",
+            "testfile_template_js"
+          ),
+          name = "testfile_template_js3.js"
+        )
+      )
+
+      # IV. test the internal ".css" file usage
+      # IV.A standard case
+      use_internal_css_file(
+        path = file.path(
+          path_dummy_golem,
+          "tmp_dump_testfiles",
+          "testfile_template_css.css"
+        )
+      )
+      test_file_download <- readLines(
+        "inst/app/www/testfile_template_css.css"
+      )
+      expect_identical(
+        test_file_download,
+        c(
+          " body {",
+          "  background-color: lightblue;",
+          "}",
+          "",
+          "h1 {",
+          "  color: white;",
+          "  text-align: center;",
+          "}",
+          "",
+          "p {",
+          "  font-family: verdana;",
+          "  font-size: 20px;",
+          "}"
+        )
+      )
+      # IV.B corner case: file already exists
+      expect_false(
+        use_internal_css_file(
+          path = file.path(
+            path_dummy_golem,
+            "tmp_dump_testfiles",
+            "testfile_template_css.css"
+          ),
+          name = "testfile_template_css.css"
+        )
+      )
+      # IV.C corner case: dir already exists
+      expect_false(
+        use_internal_css_file(
+          path = file.path(
+            path_dummy_golem,
+            "tmp_dump_testfiles",
+            "testfile_template_css.css"
+          ),
+          name = "testfile_template_css2.css",
+          dir = "inst/app/www2"
+        )
+      )
+      # IV.D corner case: file path does not have extension ".css"
+      expect_false(
+        use_internal_css_file(
+          path = file.path(
+            path_dummy_golem,
+            "tmp_dump_testfiles",
+            "testfile_template_css"
+          ),
+          name = "testfile_template_css3.css"
+        )
+      )
+
+      unlink(path_dummy_golem, recursive = TRUE)
+    }
+  )
+})