Add tests for LongExtension methods

pgpainless-core/src/test/java/openpgp/LongExtensionTest.java

@@ -0,0 +1,38 @@
+// SPDX-FileCopyrightText: 2025 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package openpgp;
+
+import org.junit.jupiter.api.Test;
+import org.pgpainless.key.util.KeyIdUtil;
+
+import java.util.Random;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class LongExtensionTest {
+
+    private final Random random = new Random();
+
+    @Test
+    public void testFromOpenPGPKeyId() {
+        long id = random.nextLong();
+        String hexId = LongExtensionsKt.openPgpKeyId(id);
+        assertEquals(16, hexId.length());
+        // Calling companion object extension methods from java is tricky.
+        // KeyIdUtil delegates to Long.Companion extension method though.
+        long parsed = KeyIdUtil.fromLongKeyId(hexId);
+        assertEquals(id, parsed, "Long MUST still match after converting to hex and back.");
+    }
+
+    @Test
+    public void testParsingMalformedHexIdFails() {
+        assertThrows(IllegalArgumentException.class, () ->
+                        KeyIdUtil.fromLongKeyId("00"),
+                "Hex encoding is too short, expect 16 chars.");assertThrows(IllegalArgumentException.class, () ->
+                        KeyIdUtil.fromLongKeyId("00010203040506XX"),
+                "Hex encoding contains non-hex chars.");
+    }
+}