Add test for PolicyAdapter properly adapting NotationRegistry implementations

pgpainless-core/src/test/java/org/bouncycastle/PolicyAdapterTest.java

@@ -0,0 +1,37 @@
+// SPDX-FileCopyrightText: 2025 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.bouncycastle;
+
+import org.bouncycastle.openpgp.api.OpenPGPPolicy;
+import org.junit.jupiter.api.Test;
+import org.pgpainless.PGPainless;
+import org.pgpainless.bouncycastle.PolicyAdapter;
+import org.pgpainless.policy.Policy;
+import org.pgpainless.util.NotationRegistry;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class PolicyAdapterTest {
+
+    @Test
+    public void testNotationRegistryAdaption() {
+        NotationRegistry pgpainlessNotationReg = new NotationRegistry();
+        pgpainlessNotationReg.addKnownNotation("foo");
+
+        Policy policy = PGPainless.getInstance().getAlgorithmPolicy()
+                .copy()
+                .withNotationRegistry(pgpainlessNotationReg)
+                .build();
+
+        PolicyAdapter adapter = new PolicyAdapter(policy);
+        OpenPGPPolicy.OpenPGPNotationRegistry bcNotationReg = adapter.getNotationRegistry();
+        assertTrue(bcNotationReg.isNotationKnown("foo"));
+        assertFalse(bcNotationReg.isNotationKnown("bar"));
+        bcNotationReg.addKnownNotation("bar");
+
+        assertTrue(pgpainlessNotationReg.isKnownNotation("bar"));
+    }
+}