diff --git a/tests/testthat/_snaps/assertions.md b/tests/testthat/_snaps/assertions.md
index a2809dbb..268fa13a 100644
--- a/tests/testthat/_snaps/assertions.md
+++ b/tests/testthat/_snaps/assertions.md
@@ -261,6 +261,15 @@
       ! List element "val" must be `>=0` in argument `input`:
       i  But, `input[[2]]$val = -1`, and `input[[3]]$val = -2`
 
+# assert_one_to_one Test 84: error if there is a one to many mapping
+
+    Code
+      assert_one_to_one(pharmaversesdtm::dm, exprs(DOMAIN), exprs(USUBJID))
+    Condition
+      Error:
+      ! For some values of "DOMAIN" there is more than one value of "USUBJID"
+      i Call `get_one_to_many_dataset()` to get all one-to-many values.
+
 # assert_date_var Test 86: error if variable is not a date or datetime variable
 
     Code
diff --git a/tests/testthat/test-assertions.R b/tests/testthat/test-assertions.R
index 87633c45..e75fb951 100644
--- a/tests/testthat/test-assertions.R
+++ b/tests/testthat/test-assertions.R
@@ -1268,6 +1268,13 @@ test_that("assert_list_element Test 83: error if the elements do not fulfill the
 ## Test 84: error if there is a one to many mapping ----
 test_that("assert_one_to_one Test 84: error if there is a one to many mapping", {
   expect_error(
+    assert_one_to_one(pharmaversesdtm::dm, exprs(DOMAIN), exprs(USUBJID)),
+    class = "assert_one_to_one"
+  )
+  admiraldev_environment$one_to_many <- NULL
+
+  expect_snapshot(
+    error = TRUE,
     assert_one_to_one(pharmaversesdtm::dm, exprs(DOMAIN), exprs(USUBJID))
   )
   admiraldev_environment$one_to_many <- NULL
@@ -1276,7 +1283,8 @@ test_that("assert_one_to_one Test 84: error if there is a one to many mapping",
 ## Test 85: error if there is a many to one mapping ----
 test_that("assert_one_to_one Test 85: error if there is a many to one mapping", {
   expect_error(
-    assert_one_to_one(pharmaversesdtm::dm, exprs(USUBJID), exprs(DOMAIN))
+    assert_one_to_one(pharmaversesdtm::dm, exprs(USUBJID), exprs(DOMAIN)),
+    class = "assert_one_to_one"
   )
   admiraldev_environment$many_to_one <- NULL
 })