added StackTraceElementProxyTest, minor edits to AGENTS.md

Signed-off-by: ceki <ceki@qos.ch>

Author: ceki

AGENTS.md

@@ -13,3 +13,11 @@
   compatibility, especially changes in interfaces or super classes.
 
 Follow these rules at all times.
+
+Maven can be located via the value of the $MAVEN_HOME environment variable. 
+Java can ve located via the value of the $JAVA_HOME environment variable.
+
+Indicate whether these values are accessible or not.
+
+If valid, always use the values of these environment variables to
+locate Maven and Java.

logback-classic/src/test/java/ch/qos/logback/classic/spi/StackTraceElementProxyTest.java

@@ -0,0 +1,151 @@
+/*
+ * Logback: the reliable, generic, fast and flexible logging framework.
+ * Copyright (C) 1999-2026, QOS.ch. All rights reserved.
+ *
+ * This program and the accompanying materials are dual-licensed under
+ * either the terms of the Eclipse Public License v2.0 as published by
+ * the Eclipse Foundation
+ *
+ *   or (per the licensee's choosing)
+ *
+ * under the terms of the GNU Lesser General Public License version 2.1
+ * as published by the Free Software Foundation.
+ */
+package ch.qos.logback.classic.spi;
+
+import ch.qos.logback.classic.ClassicConstants;
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class StackTraceElementProxyTest {
+
+    @Test
+    public void nullStackTraceElementIsReplacedByNASubstitute() {
+        StackTraceElementProxy step = new StackTraceElementProxy(null);
+
+        assertNotNull(step.getStackTraceElement());
+        assertSame(StackTraceElementProxy.NA_SUBSTITUTE, step.getStackTraceElement());
+
+        StackTraceElement ste = step.getStackTraceElement();
+        assertEquals(ClassicConstants.DECLARING_CLASS_NA, ste.getClassName());
+        assertEquals(ClassicConstants.METHOD_NAME_NA, ste.getMethodName());
+        assertEquals(ClassicConstants.FILENAME_NA, ste.getFileName());
+        assertEquals(ClassicConstants.LINE_NUMBER_NA, ste.getLineNumber());
+    }
+
+    @Test
+    public void getSTEAsStringWorksWithNullInput() {
+        StackTraceElementProxy step = new StackTraceElementProxy(null);
+        String steAsString = step.getSTEAsString();
+        assertNotNull(steAsString);
+        assertTrue(steAsString.startsWith("at "));
+        assertTrue(steAsString.contains(ClassicConstants.DECLARING_CLASS_NA));
+        assertTrue(steAsString.contains(ClassicConstants.METHOD_NAME_NA));
+    }
+
+    @Test
+    public void toStringWorksWithNullInput() {
+        StackTraceElementProxy step = new StackTraceElementProxy(null);
+        assertEquals(step.getSTEAsString(), step.toString());
+    }
+
+    @Test
+    public void hashCodeAndEqualsWorkWithNullInput() {
+        StackTraceElementProxy step1 = new StackTraceElementProxy(null);
+        StackTraceElementProxy step2 = new StackTraceElementProxy(null);
+
+        assertEquals(step1, step2);
+        assertEquals(step1.hashCode(), step2.hashCode());
+
+        StackTraceElement realSTE = new StackTraceElement("com.example.Foo", "bar", "Foo.java", 42);
+        StackTraceElementProxy step3 = new StackTraceElementProxy(realSTE);
+
+        assertNotEquals(step1, step3);
+        assertNotEquals(step1.hashCode(), step3.hashCode());
+    }
+
+    @Test
+    public void equalsHandlesNullAndDifferentClass() {
+        StackTraceElementProxy step = new StackTraceElementProxy(null);
+        assertNotEquals(null, step);
+        assertEquals(step, step);
+    }
+
+    @Test
+    public void normalNonNullStackTraceElement() {
+        StackTraceElement realSTE = new StackTraceElement("com.example.MyClass", "doSomething", "MyClass.java", 123);
+        StackTraceElementProxy step = new StackTraceElementProxy(realSTE);
+
+        assertSame(realSTE, step.getStackTraceElement());
+        assertTrue(step.getSTEAsString().startsWith("at com.example.MyClass.doSomething(MyClass.java:123)"));
+        assertEquals(step.getSTEAsString(), step.toString());
+    }
+
+    @Test
+    public void classPackagingData() {
+        StackTraceElementProxy step = new StackTraceElementProxy(null);
+
+        assertEquals(null, step.getClassPackagingData());
+
+        ClassPackagingData cpd = new ClassPackagingData("some.jar", "1.0", true);
+        step.setClassPackagingData(cpd);
+        assertSame(cpd, step.getClassPackagingData());
+
+        // second set must throw
+        assertThrows(IllegalStateException.class, () -> step.setClassPackagingData(new ClassPackagingData("x", "y")));
+
+        // packaging data affects equals
+        StackTraceElementProxy step2 = new StackTraceElementProxy(null);
+        step2.setClassPackagingData(new ClassPackagingData("some.jar", "1.0", true));
+        assertEquals(step, step2);
+
+        StackTraceElementProxy step3 = new StackTraceElementProxy(null);
+        step3.setClassPackagingData(new ClassPackagingData("other.jar", "2.0", false));
+        assertNotEquals(step, step3);
+    }
+
+    @Test
+    public void serializationRoundTripPreservesBehavior() throws IOException, ClassNotFoundException {
+        // normal STE case
+        StackTraceElement realSTE = new StackTraceElement("p.q.R", "m", "R.java", 7);
+        StackTraceElementProxy original = new StackTraceElementProxy(realSTE);
+        original.setClassPackagingData(new ClassPackagingData("loc", "ver"));
+        String originalAsString = original.getSTEAsString(); // force cache of transient
+
+        StackTraceElementProxy deserialized = roundTripSerialize(original);
+        assertEquals(original, deserialized);
+        assertEquals(originalAsString, deserialized.getSTEAsString());
+        assertEquals(original.getClassPackagingData(), deserialized.getClassPackagingData()); // deserialized instance, use equals not same
+
+        // null STE (NA_SUBSTITUTE) case
+        StackTraceElementProxy originalNull = new StackTraceElementProxy(null);
+        String originalNullAsString = originalNull.getSTEAsString();
+
+        StackTraceElementProxy deserializedNull = roundTripSerialize(originalNull);
+        assertEquals(originalNull, deserializedNull);
+        assertEquals(StackTraceElementProxy.NA_SUBSTITUTE, deserializedNull.getStackTraceElement());
+        assertEquals(originalNullAsString, deserializedNull.getSTEAsString());
+    }
+
+    private StackTraceElementProxy roundTripSerialize(StackTraceElementProxy input) throws IOException, ClassNotFoundException {
+        ByteArrayOutputStream bos = new ByteArrayOutputStream();
+        try (ObjectOutputStream oos = new ObjectOutputStream(bos)) {
+            oos.writeObject(input);
+        }
+        try (ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(bos.toByteArray()))) {
+            return (StackTraceElementProxy) ois.readObject();
+        }
+    }
+}