diff --git a/tests/testthat/test-sort.R b/tests/testthat/test-sort.R
index a1f418f8..75aa9a91 100644
--- a/tests/testthat/test-sort.R
+++ b/tests/testthat/test-sort.R
@@ -26,3 +26,80 @@ test_that("str_sort() preserves names", {
   out <- str_sort(x)
   expect_equal(names(out), c("A", "B", "C"))
 })
+
+# Edge cases for data cleaning ------------------------------------------------
+
+test_that("str_sort() handles empty input", {
+  expect_equal(str_sort(character()), character())
+  expect_equal(str_sort(character(), numeric = TRUE), character())
+})
+
+test_that("str_order() handles empty input", {
+  expect_equal(str_order(character()), integer())
+  expect_equal(str_order(character(), numeric = TRUE), integer())
+})
+
+test_that("str_rank() handles empty input", {
+  expect_equal(str_rank(character()), integer())
+  expect_equal(str_rank(character(), numeric = TRUE), integer())
+})
+
+test_that("str_sort() handles single element", {
+  expect_equal(str_sort("a"), "a")
+  expect_equal(str_sort("a", decreasing = TRUE), "a")
+})
+
+test_that("str_order() handles single element", {
+  expect_equal(str_order("a"), 1L)
+  expect_equal(str_order("a", decreasing = TRUE), 1L)
+})
+
+test_that("str_rank() handles single element", {
+  expect_equal(str_rank("a"), 1L)
+})
+
+test_that("str_sort() handles all NA input", {
+  expect_equal(str_sort(c(NA, NA, NA)), c(NA, NA, NA))
+  expect_equal(
+    str_sort(c(NA, NA, NA), na_last = TRUE),
+    c(NA, NA, NA)
+  )
+  expect_equal(
+    str_sort(c(NA, NA, NA), na_last = FALSE),
+    c(NA, NA, NA)
+  )
+})
+
+test_that("str_sort() drops NAs when na_last = NA", {
+  x <- c("b", NA, "a")
+  expect_equal(str_sort(x, na_last = NA), c("a", "b"))
+})
+
+test_that("str_sort() handles decreasing order", {
+  x <- c("a", "b", "c")
+  expect_equal(str_sort(x, decreasing = TRUE), c("c", "b", "a"))
+})
+
+test_that("str_order() handles decreasing order", {
+  x <- c("a", "b", "c")
+  expect_equal(str_order(x, decreasing = TRUE), c(3L, 2L, 1L))
+})
+
+test_that("str_sort() handles mixed case", {
+  x <- c("B", "a", "C")
+  # Default locale sorts case-sensitive (upper before lower in en locale)
+  out <- str_sort(x)
+  expect_equal(out[1], "a")
+})
+
+test_that("str_order() preserves names", {
+  x <- c(C = "3", B = "2", A = "1")
+  out <- str_order(x)
+  expect_equal(names(x[out]), c("A", "B", "C"))
+})
+
+test_that("str_sort() handles single NA", {
+  expect_equal(str_sort(NA_character_), NA_character_)
+  expect_equal(str_sort(c("a", NA, "b"), na_last = TRUE), c("a", "b", NA))
+  expect_equal(str_sort(c("a", NA, "b"), na_last = FALSE), c(NA, "a", "b"))
+})