From 763040d5f94d40c8b8705c55b886e49ac8076204 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A1s=20B=20Nagy?=
 <20251272+BNAndras@users.noreply.github.com>
Date: Mon, 5 Jan 2026 21:15:06 -0800
Subject: [PATCH] Sync `isbn-verifier` tests

---
 exercises/practice/isbn-verifier/.meta/tests.toml      | 6 ++++++
 exercises/practice/isbn-verifier/isbn-verifier.spec.js | 8 ++++++++
 2 files changed, 14 insertions(+)

diff --git a/exercises/practice/isbn-verifier/.meta/tests.toml b/exercises/practice/isbn-verifier/.meta/tests.toml
index 6d5a845990..17e18d47ac 100644
--- a/exercises/practice/isbn-verifier/.meta/tests.toml
+++ b/exercises/practice/isbn-verifier/.meta/tests.toml
@@ -30,6 +30,12 @@ description = "invalid character in isbn is not treated as zero"
 [28025280-2c39-4092-9719-f3234b89c627]
 description = "X is only valid as a check digit"
 
+[8005b57f-f194-44ee-88d2-a77ac4142591]
+description = "only one check digit is allowed"
+
+[fdb14c99-4cf8-43c5-b06d-eb1638eff343]
+description = "X is not substituted by the value 10"
+
 [f6294e61-7e79-46b3-977b-f48789a4945b]
 description = "valid isbn without separating dashes"
 
diff --git a/exercises/practice/isbn-verifier/isbn-verifier.spec.js b/exercises/practice/isbn-verifier/isbn-verifier.spec.js
index 6ff9dedbf8..99d2cbf419 100644
--- a/exercises/practice/isbn-verifier/isbn-verifier.spec.js
+++ b/exercises/practice/isbn-verifier/isbn-verifier.spec.js
@@ -30,6 +30,14 @@ describe('ISBN Verifier', () => {
     expect(isValid('3-598-2X507-9')).toEqual(false);
   });
 
+  xtest('only one check digit is allowed', () => {
+    expect(isValid('3-598-21508-96')).toEqual(false);
+  });
+
+  xtest('X is not substituted by the value 10', () => {
+    expect(isValid('3-598-2X507-5')).toEqual(false);
+  });
+
   xtest('valid isbn without separating dashes', () => {
     expect(isValid('3598215088')).toEqual(true);
   });