diff --git a/tests/testthat/test-ard_car_vif.R b/tests/testthat/test-ard_car_vif.R
index 930ad5155..34ea2df7b 100644
--- a/tests/testthat/test-ard_car_vif.R
+++ b/tests/testthat/test-ard_car_vif.R
@@ -19,7 +19,7 @@ test_that("ard_car_vif() appropriate errors are given for model with only 1 term
     lm(AGE ~ ARM, data = cards::ADSL) |>
       ard_car_vif() |>
       dplyr::select(error) %>%
-      is.null,
+      is.null(),
     FALSE
   )
 })
diff --git a/tests/testthat/test-ard_effectsize_cohens_d.R b/tests/testthat/test-ard_effectsize_cohens_d.R
index da050ceeb..cf846afe0 100644
--- a/tests/testthat/test-ard_effectsize_cohens_d.R
+++ b/tests/testthat/test-ard_effectsize_cohens_d.R
@@ -28,9 +28,9 @@ test_that("ard_effectsize_cohens_d() works", {
   # errors are properly handled
   expect_equal(
     cards::ADSL |>
-      ard_effectsize_cohens_d(by = ARM, variables = AGE)  |>
+      ard_effectsize_cohens_d(by = ARM, variables = AGE) |>
       dplyr::select(error) %>%
-      is.null,
+      is.null(),
     FALSE
   )
 
@@ -91,7 +91,7 @@ test_that("ard_effectsize_paired_cohens_d() works", {
       ) |>
       ard_effectsize_paired_cohens_d(by = ARM, variable = AGE, id = USUBJID) |>
       dplyr::select(error) %>%
-      is.null,
+      is.null(),
     FALSE
   )
 })
diff --git a/tests/testthat/test-ard_effectsize_hedges_g.R b/tests/testthat/test-ard_effectsize_hedges_g.R
index 3d5057e5e..3bd0024e0 100644
--- a/tests/testthat/test-ard_effectsize_hedges_g.R
+++ b/tests/testthat/test-ard_effectsize_hedges_g.R
@@ -28,7 +28,7 @@ test_that("ard_effectsize_hedges_g() works", {
     cards::ADSL |>
       ard_effectsize_hedges_g(by = ARM, variable = AGE) |>
       dplyr::select(error) %>%
-      is.null,
+      is.null(),
     FALSE
   )
 
@@ -91,7 +91,7 @@ test_that("ard_effectsize_paired_hedges_g() works", {
       ) |>
       ard_effectsize_paired_hedges_g(by = ARM, variable = AGE, id = USUBJID) |>
       dplyr::select(error) %>%
-      is.null,
+      is.null(),
     FALSE
   )
 })
diff --git a/tests/testthat/test-ard_stats_t_test.R b/tests/testthat/test-ard_stats_t_test.R
index 5bd573bf6..9e487906a 100644
--- a/tests/testthat/test-ard_stats_t_test.R
+++ b/tests/testthat/test-ard_stats_t_test.R
@@ -48,7 +48,7 @@ test_that("ard_stats_t_test() works", {
     cards::ADSL |>
       ard_stats_t_test(by = ARM, variable = AGE, var.equal = TRUE) |>
       dplyr::select(error) %>%
-      is.null,
+      is.null(),
     FALSE
   )
 
@@ -111,7 +111,7 @@ test_that("ard_stats_paired_t_test() works", {
       ) |>
       ard_stats_paired_t_test(by = ARM, variable = AGE, id = USUBJID, var.equal = TRUE) |>
       dplyr::select(error) %>%
-      is.null,
+      is.null(),
     FALSE
   )
 })