From 6d1dba5cd015073e467d9dd4fdcca6aa7def516e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A1s=20B=20Nagy?=
 <20251272+BNAndras@users.noreply.github.com>
Date: Sun, 4 Jan 2026 18:34:22 -0800
Subject: [PATCH] Sync `isbn-verifier` tests

---
 exercises/practice/isbn-verifier/.meta/tests.toml          | 6 ++++++
 exercises/practice/isbn-verifier/isbn-verifier.spec.coffee | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/exercises/practice/isbn-verifier/.meta/tests.toml b/exercises/practice/isbn-verifier/.meta/tests.toml
index 6d5a845..17e18d4 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.coffee b/exercises/practice/isbn-verifier/isbn-verifier.spec.coffee
index 30f612f..aef7751 100644
--- a/exercises/practice/isbn-verifier/isbn-verifier.spec.coffee
+++ b/exercises/practice/isbn-verifier/isbn-verifier.spec.coffee
@@ -23,6 +23,12 @@ describe  'ISBN Verifier', ->
   xit 'X is only valid as a check digit', ->
     expect(IsbnVerifier.isValid '3-598-2X507-9').toEqual false
 
+  xit 'only one check digit is allowed', ->
+    expect(IsbnVerifier.isValid '3-598-21508-96').toEqual false
+
+  xit 'X is not substituted by the value 10', ->
+    expect(IsbnVerifier.isValid '3-598-2X507-5').toEqual false
+
   xit 'valid ISBN without separating dashes', ->
     expect(IsbnVerifier.isValid '3598215088').toEqual true