Unify tests between log4j-appender-2.17 javaagent and library instrumentation

[Copilot]

Plan: Unify tests between log4j-appender-2.17 javaagent and library instrumentation

Based on my analysis of the repository structure and the issue requirements, I will:

• Create a testing module under instrumentation/log4j/log4j-appender-2.17/
• Extract common test code from both javaagent and library tests into the testing module
• Create a base test class that both javaagent and library tests can extend
• Update javaagent tests to extend the base test class
• Add new library test that extends the base test class
• Remove duplicative tests from AbstractOpenTelemetryAppenderTest
• Add the testing module as a test dependency to both javaagent and library modules
• Register the testing module in settings.gradle.kts
• Fix library test configuration to match javaagent behavior (log level, logger config)
• Update test assertions to be flexible for both javaagent and library implementations
• Refactor addCodeLocationAttributes to only handle code location attributes
• Remove unnecessary dependencies (auto-value, explicit log4j-api)
• Optimize log4j-core dependency scope (compileOnly vs api)

Summary

Successfully created a unified testing module for log4j-appender-2.17 that contains shared test code (AbstractLog4j2Test) which both javaagent and library instrumentation can extend. This follows the pattern used by other instrumentations in the repository (e.g., jsf-jakarta-common).

Key Changes:

1. New testing module with shared AbstractLog4j2Test base class containing common tests
2. Simplified javaagent test - now just extends the base class
3. New library test - extends the base class to run the same tests
4. Removed duplicative tests - AbstractOpenTelemetryAppenderTest now contains only library-specific tests (initializeWithBuilder), while common tests (logContextData, logStringMapMessage, etc.) are unified in AbstractLog4j2Test
5. Updated log4j2.xml - configured "abc" logger to match test expectations (kept TestLogger for remaining library-specific tests)
6. Flexible assertions - handles differences between javaagent and library (async logging, code attributes)
7. Proper separation of concerns - addCodeLocationAttributes only handles code location, thread and test-specific attributes added separately
8. Minimal dependencies - removed unnecessary auto-value and explicit log4j-api dependencies, optimized log4j-core to compileOnly

Both javaagent and library now share the same test suite, significantly reducing code duplication and ensuring consistent behavior. Library-specific tests (builder API, log replay, span propagation) remain in their respective test classes.

Fixes #4956

Original prompt

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This section details on the original issue you should resolve

<issue_title>Unify tests between log4j-appender-2.16 javaagent and library instrumentation</issue_title>
<issue_description>Need to introduce testing module and have single (base) test for both javaagent and library instrumentation.</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #4956

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[otelbot-java-instrumentation]

🔧 The result from spotlessApply was committed to the PR branch.

[trask]

superseded by #14859