Refactor before entitlements for testing

libs/entitlement/src/test/java/org/elasticsearch/entitlement/BridgeUtilTests.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+package org.elasticsearch.entitlement;
+
+import org.elasticsearch.entitlement.bridge.Util;
+import org.elasticsearch.test.ESTestCase;
+
+import static org.elasticsearch.entitlement.BridgeUtilTests.MockSensitiveClass.mockSensitiveMethod;
+
+/**
+ * Note: this is not un the bridge package because that is a uniquely bad one to use for tests.
+ * Since:
+ * <ol>
+ *     <li>
+ *         we much patch the bridge module into {@code java.base} for it to be reachable
+ *         from JDK methods,
+ *     </li>
+ *     <li>
+ *         the bridge module exports {@code org.elasticsearch.entitlement.bridge}, and
+ *     </li>
+ *     <li>
+ *         Java forbids split packages
+ *     </li>
+ * </ol>
+ *
+ * ...therefore, we'll be unable to load any tests in the {@code org.elasticsearch.entitlement.bridge}
+ * package from the classpath.
+ * <p>
+ * Hence, we put this test in another package. It's still accessible during testing, though,
+ * because we export the bridge to `ALL-UNNAMED` anyway.
+ */
+public class BridgeUtilTests extends ESTestCase {
+
+    public void testCallerClass() {
+        assertEquals(BridgeUtilTests.class, mockSensitiveMethod());
+    }
+
+    /**
+     * A separate class so the stack walk can discern the sensitive method's own class
+     * from that of its caller.
+     */
+    static class MockSensitiveClass {
+        public static Class<?> mockSensitiveMethod() {
+            return Util.getCallerClass();
+        }
+    }
+
+}