diff --git a/R/assert-version.R b/R/assert-version.R
index 4aea58f..07c262f 100644
--- a/R/assert-version.R
+++ b/R/assert-version.R
@@ -86,10 +86,10 @@ assert_version_package <- function(
 
   installation_message <-
     if (1L <= nchar(installation_code)) {
-      "  Install the package with `%s`." |>
+      "  Install the package with `%s`.  Afterwards, please restart the R session." |>
         sprintf(installation_code)
     } else {
-      ""
+      "  Afterwards, please restart the R session."
     }
 
   if (!package_is_installed) {
diff --git a/tests/testthat/test-assert-version-package.R b/tests/testthat/test-assert-version-package.R
index 2c8dd08..3b50ffc 100644
--- a/tests/testthat/test-assert-version-package.R
+++ b/tests/testthat/test-assert-version-package.R
@@ -14,7 +14,7 @@ test_that("old minimum", {
   expect_true(r)
 })
 
-test_that("minimum that throws an error", {
+test_that("minimum that throws an error -base", {
   expected_error_message <- "Your version of the `base` package is too old"
   expect_error(
     assert_version_package("base", "99.1.0"),
@@ -26,5 +26,28 @@ test_that("minimum that throws an error", {
     expected_error_message
   )
 })
-stop("TODO: test installation message for non-existent package.")
-stop("TODO: test installation message for an old package.")
+test_that("minimum that throws an error -tibble", {
+  expected_error_message <- "Your version of the `tibble` package is too old"
+  expect_error(
+    assert_version_package("tibble", "99.1.0"),
+    expected_error_message
+  )
+
+  expect_error(
+    assert_version_package("tibble", package_version("99.1.0")),
+    expected_error_message
+  )
+})
+test_that("missing package throws an error", {
+  expected_error_message <- "The package 'tibbleeee' not installed\\.  Afterwards, please restart the R session\\."
+
+  expect_error(
+    assert_version_package("tibbleeee", "99.1.0"),
+    expected_error_message
+  )
+
+  expect_error(
+    assert_version_package("tibbleeee", "99.1.0"),
+    expected_error_message
+  )
+})