isbn-verifier: update tests (#2108)

Author: senekor

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"
 

exercises/practice/isbn-verifier/tests/isbn_verifier.rs

@@ -41,6 +41,18 @@ fn x_is_only_valid_as_a_check_digit() {
     assert!(!is_valid_isbn("3-598-2X507-9"));
 }
 
+#[test]
+#[ignore]
+fn only_one_check_digit_is_allowed() {
+    assert!(!is_valid_isbn("3-598-21508-96"));
+}
+
+#[test]
+#[ignore]
+fn x_is_not_substituted_by_the_value_10() {
+    assert!(!is_valid_isbn("3-598-2X507-5"));
+}
+
 #[test]
 #[ignore]
 fn valid_isbn_without_separating_dashes() {