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test(log4j2): Add initial test suite covering plugin registration (#615)
This package previously had no tests and no JUnit dependency. Add JUnit Jupiter, the surefire plugin, and an initial test class that exercises the full plugin resolution path end-to-end: a log4j2.xml on the test classpath, a real LogManager-issued logger, and stdout capture (LambdaAppender writes through LambdaRuntime.getLogger() to System.out). The TEXT test routes the root logger through LambdaTextFormat with a deterministic PatternLayout and asserts each level appears. The JSON test adds a second LambdaAppender with format="JSON" backed by JsonTemplateLayout + LambdaLayout.json, attached via additivity=false to a "json-test" logger, and asserts the messages show up JSON-encoded. Add log4j-layout-template-json at test scope so the JSON path can resolve at test time. Users are still expected to bring their own copy at runtime (peer-dependency model, like PatternLayout); the published artifact's dependency surface is unchanged. The tests succeed on Java 8 and fail on Java 25, because annotation processors are not run by default on Java 25, Log4j2Plugins.dat is not generated for our plugins, and both tests surface the resulting CLASS_NOT_FOUND from the log4j status logger.
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‎aws-lambda-java-log4j2/pom.xml‎

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<maven.compiler.source>1.8</maven.compiler.source>
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<maven.compiler.target>1.8</maven.compiler.target>
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<log4j.version>2.25.4</log4j.version>
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<junit-jupiter.version>5.12.2</junit-jupiter.version>
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</properties>
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<distributionManagement>
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<artifactId>log4j-api</artifactId>
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<version>${log4j.version}</version>
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</dependency>
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<dependency>
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<groupId>org.apache.logging.log4j</groupId>
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<artifactId>log4j-layout-template-json</artifactId>
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<version>${log4j.version}</version>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.junit.jupiter</groupId>
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<artifactId>junit-jupiter-engine</artifactId>
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<version>${junit-jupiter.version}</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-surefire-plugin</artifactId>
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<version>3.5.2</version>
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</plugin>
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</plugins>
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</build>
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<profiles>
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<profile>
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<id>dev</id>
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</build>
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</profile>
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</profiles>
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</project>
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</project>

‎aws-lambda-java-log4j2/src/test/java/com/amazonaws/services/lambda/runtime/log4j2/LambdaAppenderPluginTest.java‎

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/* Copyright 2026 Amazon.com, Inc. or its affiliates. All Rights Reserved. */
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package com.amazonaws.services.lambda.runtime.log4j2;
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import org.apache.logging.log4j.LogManager;
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import org.apache.logging.log4j.Logger;
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import org.junit.jupiter.api.AfterEach;
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import org.junit.jupiter.api.BeforeEach;
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import org.junit.jupiter.api.Test;
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import java.io.ByteArrayOutputStream;
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import java.io.PrintStream;
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import java.io.UnsupportedEncodingException;
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import java.nio.charset.StandardCharsets;
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import static org.junit.jupiter.api.Assertions.assertFalse;
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import static org.junit.jupiter.api.Assertions.assertTrue;
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public class LambdaAppenderPluginTest {
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private final PrintStream originalOut = System.out;
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private ByteArrayOutputStream captured;
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@BeforeEach
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void redirectStdout() throws UnsupportedEncodingException {
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captured = new ByteArrayOutputStream();
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System.setOut(new PrintStream(captured, true, StandardCharsets.UTF_8.name()));
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}
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@AfterEach
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void restoreStdout() {
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System.setOut(originalOut);
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}
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@Test
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void lambdaAppenderEmitsLogsAtVariousLevels() throws UnsupportedEncodingException {
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Logger logger = LogManager.getLogger(LambdaAppenderPluginTest.class);
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logger.debug("debug-msg");
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logger.info("info-msg");
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logger.warn("warn-msg");
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logger.error("error-msg");
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String output = captured.toString(StandardCharsets.UTF_8.name());
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// The PatternLayout in src/test/resources/log4j2.xml is "%-5p %c{1} - %m%n",
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// so each event should appear as "<LEVEL> LambdaAppenderPluginTest - <message>".
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assertTrue(output.contains("DEBUG LambdaAppenderPluginTest - debug-msg"),
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"expected DEBUG line in output but got:\n" + output);
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assertTrue(output.contains("INFO LambdaAppenderPluginTest - info-msg"),
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"expected INFO line in output but got:\n" + output);
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assertTrue(output.contains("WARN LambdaAppenderPluginTest - warn-msg"),
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"expected WARN line in output but got:\n" + output);
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assertTrue(output.contains("ERROR LambdaAppenderPluginTest - error-msg"),
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"expected ERROR line in output but got:\n" + output);
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// Sanity check: log4j should not have fallen back to its default
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// ConsoleAppender / status logger error message.
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assertFalse(output.contains("ERROR StatusLogger"),
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"log4j status logger reported an error, output was:\n" + output);
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}
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@Test
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void lambdaAppenderEmitsJsonForJsonFormatLogger() throws UnsupportedEncodingException {
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// The "json-test" logger is configured in src/test/resources/log4j2.xml
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// with additivity=false to a second LambdaAppender using format="JSON"
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// and JsonTemplateLayout backed by LambdaLayout.json.
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Logger logger = LogManager.getLogger("json-test");
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logger.info("json-info-msg");
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logger.error("json-error-msg");
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String output = captured.toString(StandardCharsets.UTF_8.name());
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assertTrue(output.contains("json-info-msg"),
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"expected json-info-msg in output but got:\n" + output);
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assertTrue(output.contains("json-error-msg"),
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"expected json-error-msg in output but got:\n" + output);
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// Output should look like JSON, not the text PatternLayout from the
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// root logger — so it must contain JSON field punctuation around the
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// message rather than the "INFO json-test - ..." text pattern.
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assertTrue(output.contains("\"message\":\"json-info-msg\""),
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"expected JSON-encoded message field but got:\n" + output);
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}
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}

‎aws-lambda-java-log4j2/src/test/resources/log4j2.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<Configuration status="WARN">
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<Appenders>
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<Lambda name="LambdaText" format="TEXT">
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<LambdaTextFormat>
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<PatternLayout>
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<pattern>%-5p %c{1} - %m%n</pattern>
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</PatternLayout>
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</LambdaTextFormat>
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</Lambda>
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<Lambda name="LambdaJson" format="JSON">
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<LambdaJsonFormat>
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<JsonTemplateLayout eventTemplateUri="classpath:LambdaLayout.json" />
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</LambdaJsonFormat>
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</Lambda>
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</Appenders>
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<Loggers>
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<Logger name="json-test" level="DEBUG" additivity="false">
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<AppenderRef ref="LambdaJson" />
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</Logger>
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<Root level="DEBUG">
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<AppenderRef ref="LambdaText" />
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</Root>
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</Loggers>
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</Configuration>

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