test: extend unit tests to cover KeyMapWrapper error conditions

Claude 4 wrote the original tests; I then replaced its fix (which incorrectly
also propagated errors in GetKey for KeyMap), updated the tests, and removed
some extra tests which seemed uninformative and just noisy.

To backport this to 12.x, just do s/KeyMap/KeyMapWrapper/ on the new tests.
Oh, and add some `let keymap = KeyMapWrapper::from(keymap)` lines.

Co-authored-by: aider (anthropic/claude-sonnet-4-20250514) <aider@aider.chat>

Author: apoelstra

src/descriptor/key_map.rs

@@ -336,4 +336,81 @@ mod tests {
 
         assert_eq!(pk, expected_pk);
     }
+
+    #[test]
+    fn get_key_keymap_no_match() {
+        let secp = Secp256k1::new();
+
+        // Create a keymap with one key
+        let descriptor_s = "wpkh(cMk8gWmj1KpjdYnAWwsEDekodMYhbyYBhG8gMtCCxucJ98JzcNij)";
+        let (_, keymap) = Descriptor::parse_descriptor(&secp, &descriptor_s).unwrap();
+
+        // Request a different public key that doesn't exist in the keymap
+        let different_sk =
+            PrivateKey::from_str("cNJFgo1driFnPcBdBX8BrJrpxchBWXwXCvNH5SoSkdcF6JXXwHMm").unwrap();
+        let different_pk = different_sk.public_key(&secp);
+        let request = KeyRequest::Pubkey(different_pk);
+
+        let result = keymap.get_key(request, &secp).unwrap();
+        assert!(result.is_none(), "Should return None when no matching key is found");
+    }
+
+    #[test]
+    fn get_key_descriptor_secret_key_xonly_not_supported() {
+        let secp = Secp256k1::new();
+
+        let descriptor_sk = DescriptorSecretKey::from_str("xprv9s21ZrQH143K3QTDL4LXw2F7HEK3wJUD2nW2nRk4stbPy6cq3jPPqjiChkVvvNKmPGJxWUtg6LnF5kejMRNNU3TGtRBeJgk33yuGBxrMPHi").unwrap();
+
+        // Create an x-only public key request
+        let sk =
+            PrivateKey::from_str("cMk8gWmj1KpjdYnAWwsEDekodMYhbyYBhG8gMtCCxucJ98JzcNij").unwrap();
+        let xonly_pk = sk.public_key(&secp).inner.x_only_public_key().0;
+        let request = KeyRequest::XOnlyPubkey(xonly_pk);
+
+        let result = descriptor_sk.get_key(request.clone(), &secp);
+        assert!(matches!(result, Err(GetKeyError::NotSupported)));
+
+        // Also test with KeyMap
+        let descriptor_s = "wpkh(xprv9s21ZrQH143K3QTDL4LXw2F7HEK3wJUD2nW2nRk4stbPy6cq3jPPqjiChkVvvNKmPGJxWUtg6LnF5kejMRNNU3TGtRBeJgk33yuGBxrMPHi)";
+        let (_, keymap) = Descriptor::parse_descriptor(&secp, &descriptor_s).unwrap();
+
+        // While requesting an x-only key from an individual xpriv, that's an error.
+        // But from a keymap, which might have both x-only keys and regular xprivs,
+        // we treat errors as "key not found".
+        let result = keymap.get_key(request, &secp);
+        assert!(matches!(result, Ok(None)));
+    }
+
+    #[test]
+    fn get_key_descriptor_secret_key_xonly_multipath() {
+        let secp = Secp256k1::new();
+
+        let descriptor_sk = DescriptorSecretKey::from_str("[d34db33f/84h/0h/0h]tprv8ZgxMBicQKsPd3EupYiPRhaMooHKUHJxNsTfYuScep13go8QFfHdtkG9nRkFGb7busX4isf6X9dURGCoKgitaApQ6MupRhZMcELAxTBRJgS/<0;1>").unwrap();
+
+        // Request with a different fingerprint
+        let different_fingerprint = bitcoin::bip32::Fingerprint::from([0x12, 0x34, 0x56, 0x78]);
+        let path = DerivationPath::from_str("84'/1'/0'/0").unwrap();
+        let request = KeyRequest::Bip32((different_fingerprint, path));
+
+        let result = descriptor_sk.get_key(request.clone(), &secp).unwrap();
+        assert!(result.is_none(), "Should return None when fingerprint doesn't match");
+
+        // Create an x-only public key request -- now we get "not supported".
+        let sk =
+            PrivateKey::from_str("cMk8gWmj1KpjdYnAWwsEDekodMYhbyYBhG8gMtCCxucJ98JzcNij").unwrap();
+        let xonly_pk = sk.public_key(&secp).inner.x_only_public_key().0;
+        let request_x = KeyRequest::XOnlyPubkey(xonly_pk);
+
+        let result = descriptor_sk.get_key(request_x.clone(), &secp);
+        assert!(matches!(result, Err(GetKeyError::NotSupported)));
+
+        // Also test with KeyMap; as in the previous test, the error turns to None.
+        let descriptor_s = "wpkh([d34db33f/84h/1h/0h]tprv8ZgxMBicQKsPd3EupYiPRhaMooHKUHJxNsTfYuScep13go8QFfHdtkG9nRkFGb7busX4isf6X9dURGCoKgitaApQ6MupRhZMcELAxTBRJgS/*)";
+        let (_, keymap) = Descriptor::parse_descriptor(&secp, &descriptor_s).unwrap();
+
+        let result = keymap.get_key(request, &secp).unwrap();
+        assert!(result.is_none(), "Should return None when fingerprint doesn't match");
+        let result = keymap.get_key(request_x, &secp).unwrap();
+        assert!(result.is_none(), "Should return None even on error");
+    }
 }