diff --git a/R/dplyr-plus.R b/R/dplyr-plus.R
index 47bb692..542bfeb 100644
--- a/R/dplyr-plus.R
+++ b/R/dplyr-plus.R
@@ -156,12 +156,14 @@ slice_group_sample <- function(data, group_var = NULL, n_groups = 1) {
     data <- dplyr::group_by(data, {{ group_var }})
   }
   if (!dplyr::is_grouped_df(data)) {
+    # nocov: start
     cli::cli_abort(
       c(
         "Not supposed to happen"
       ),
       .internal = TRUE
     )
+    # nocov: end
   }
   # Assuming the data is grouped now.
   group_var_name <- dplyr::group_vars(data)
@@ -353,8 +355,7 @@ extract_cell_value <- function(data, var, filter, name = NULL, length = NULL, un
   if (!is.null(length) && !rlang::has_length(res2, length)) {
     # TODO use `check_length()` when implemented. r-lib/rlang#1618
     cli::cli_abort(c(
-      "Expected an output of {length}",
-      "Got an output of {length(res2)}"
+      "Expected an output of length {length}, not {length(res2)}."
     ))
   }
 
diff --git a/tests/testthat/_snaps/dplyr-plus.md b/tests/testthat/_snaps/dplyr-plus.md
index 5c1f8b1..ec218cf 100644
--- a/tests/testthat/_snaps/dplyr-plus.md
+++ b/tests/testthat/_snaps/dplyr-plus.md
@@ -63,6 +63,14 @@
       2 1       344.  24.6
       3 All vs  643.  20.1
 
+# extract_cell_value() works
+
+    Code
+      extract_cell_value(dat, x >= 2, var = y, length = 1)
+    Condition
+      Error in `extract_cell_value()`:
+      ! Expected an output of length 1, not 2.
+
 # slice_min_max() works
 
     Code
diff --git a/tests/testthat/test-dplyr-plus.R b/tests/testthat/test-dplyr-plus.R
index 12f87aa..1f88b45 100644
--- a/tests/testthat/test-dplyr-plus.R
+++ b/tests/testthat/test-dplyr-plus.R
@@ -151,6 +151,30 @@ test_that("summarise_with_total() keeps factors", {
   expect_equal(levels(res$vs), c("Total", "0", "1"))
 })
 
+test_that("extract_cell_value() works", {
+  dat <- data.frame(
+    x = c(1, 2, 3),
+    y = c(1.5, 3, 3.5),
+    row.names = c("row1", "row2", "row4")
+  )
+  expect_equal(
+    extract_cell_value(
+      dat,
+      x == 2,
+      var = y
+    ),
+    c("row2" = 3)
+  )
+  expect_snapshot(error = TRUE,
+    extract_cell_value(
+      dat,
+      x >= 2,
+      var = y,
+      length = 1
+    )
+  )
+})
+
 test_that("slice_min_max() works", {
   expect_snapshot({
     slice_min_max(mtcars, mpg, n = 3)
@@ -160,6 +184,9 @@ test_that("slice_min_max() works", {
     nrow(slice_min_max(mtcars, mpg, with_ties = FALSE, n = 2, each = FALSE)),
     2
   )
+  expect_equal(
+    nrow(slice_min_max(mtcars, mpg, with_ties = FALSE)),
+    2)
 })
 
 test_that("na_if2() works with expr and values", {