diff --git a/tests/testthat/test-trim.R b/tests/testthat/test-trim.R
index a4b45972..61fb1f73 100644
--- a/tests/testthat/test-trim.R
+++ b/tests/testthat/test-trim.R
@@ -21,6 +21,36 @@ test_that("str_squish removes excess spaces from all parts of string", {
   expect_equal(str_squish("\ta\t bc\t"), "a bc")
 })
 
+test_that("str_trim handles NA values", {
+  expect_equal(str_trim(NA), NA_character_)
+  expect_equal(str_trim(c(NA, " abc ")), c(NA, "abc"))
+  expect_equal(str_trim(NA, "left"), NA_character_)
+  expect_equal(str_trim(NA, "right"), NA_character_)
+})
+
+test_that("str_squish handles NA values", {
+  expect_equal(str_squish(NA), NA_character_)
+  expect_equal(str_squish(c(NA, "  a  b  ")), c(NA, "a b"))
+})
+
+test_that("str_trim handles empty strings", {
+  expect_equal(str_trim(""), "")
+  expect_equal(str_trim("   "), "")
+})
+
+test_that("str_squish handles empty strings", {
+  expect_equal(str_squish(""), "")
+  expect_equal(str_squish("   "), "")
+})
+
+test_that("str_squish handles newlines and mixed whitespace", {
+  expect_equal(str_squish("a\n\nb"), "a b")
+  expect_equal(str_squish("\na\n"), "a")
+  expect_equal(str_squish("a\r\nb"), "a b")
+  expect_equal(str_squish("a\t\n b"), "a b")
+  expect_equal(str_squish("\t\n a \n\t b \t\n"), "a b")
+})
+
 test_that("trimming functions preserve names", {
   x <- c(C = "3", B = "2", A = "1")
   expect_equal(names(str_trim(x)), names(x))