Add "afterburner-tests"; enhanced Afterburner-for-classpath tests

afterburner-tests/README.md

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+# jackson-module-afterburner-tests
+
+Classpath-mode integration tests for `jackson-module-afterburner`. **This module is
+test-only and is never published.**
+
+## Why this module exists
+
+Afterburner's most valuable optimizations come from bytecode injection:
+`PropertyMutatorCollector`, `PropertyAccessorCollector`, and `CreatorOptimizer`
+generate custom mutator / accessor / instantiator classes in the *target bean's
+package* and install them on the bean's `ClassLoader`. This only works when the
+target package is not sealed.
+
+In Jackson 3.x every module descriptor — including afterburner's own test module
+— is a named JPMS module, and the JVM automatically seals every package inside a
+named module. As a result, every POJO defined inside `tools.jackson.module.afterburner`
+test sources fails the `MyClassLoader.canAddClassInPackageOf` check, and afterburner
+silently falls back to plain reflection. That means **none** of afterburner's
+injection paths are exercised by the in-tree afterburner test suite — the optimized
+code path is effectively dead weight in CI even though the tests appear to pass.
+
+This module closes that gap. It lives alongside the afterburner module but
+deliberately:
+
+- has **no `module-info.java`** in either main or test sources,
+- is configured (`useModulePath=false`) to run its tests on the classpath,
+- and therefore loads its test POJOs into the **unnamed module**, whose packages
+  are not sealed.
+
+Afterburner's injection pipeline runs on those POJOs normally, and the tests here
+verify via reflection on databind internals that each property was actually
+replaced with an `OptimizedSettableBeanProperty` / `OptimizedBeanPropertyWriter`
+and each default-creator POJO got an `OptimizedValueInstantiator`.
+
+## Do not add a `module-info.java` here
+
+Adding a module descriptor would put these test POJOs back into a named module,
+re-seal their packages, and silently turn this whole module into dead weight —
+same as the in-tree afterburner tests.
+
+If a future cleanup pass wants to "unify" the project layout by making every
+module JPMS-consistent, this one is the exception. Read this file before doing
+that.
+
+## Do not publish this module
+
+Several parent-POM plugin bindings are unbound or skipped in `pom.xml` so that
+`mvn install` on this module produces no jar, no SBOM, no Gradle module metadata,
+and no OSGi bundle. The module exists purely to run tests. If you rename an
+execution override in `pom.xml`, re-verify with:
+
+```
+./mvnw help:effective-pom -pl afterburner-tests
+```
+
+A typo in an execution id turns into silent dead config and leaves stale
+artifacts in `target/` rather than a build error.
+
+## What is covered
+
+- `PropertyMutatorCollector` — int, long, boolean, and reference-type
+  specializations for both public-field and setter-method access
+  (`MutatorSpecializationsTest`).
+- `PropertyAccessorCollector` — writer replacement on the serializer side
+  (`SerializerInjectionTest`).
+- `CreatorOptimizer` — default-constructor and static-factory positive cases,
+  plus property-based `@JsonCreator` negative case (`CreatorOptimizerTest`).
+- `MyClassLoader.defineClass` — transitively exercised by all of the above.
+
+## What is *not* covered
+
+- Private-class guard (`_classLoader != null && isPrivate(beanClass)`).
+- `setUseValueClassLoader(false)` toggle.
+- Concurrent deserializer construction.
+- Fallback path when afterburner correctly refuses to optimize (e.g. a bean
+  whose package really is sealed — the in-tree afterburner tests inadvertently
+  cover this).
+- GraalVM native-image disable path in `AfterburnerModule.setupModule`.
+
+## Known findings from this module
+
+### Afterburner parent-classloader caching silently broken on Java 9+ (#348)
+
+While writing `GeneratedClassCachingTest`, we discovered that Afterburner's
+parent-classloader cache — the mechanism that's supposed to make two
+independent `ObjectMapper` instances share a single generated mutator class
+per POJO — does not work on Java 9+ unless the JVM is launched with
+`--add-opens java.base/java.lang=ALL-UNNAMED`. `MyClassLoader` reflects into
+`ClassLoader#findLoadedClass` and `ClassLoader#defineClass`, both protected
+members of `java.lang.ClassLoader`; on modern JDKs the reflective access
+throws `InaccessibleObjectException`, which Afterburner catches silently and
+falls back to defining each generated class in a fresh throwaway loader.
+
+That's why this module's `pom.xml` sets
+`--add-opens java.base/java.lang=ALL-UNNAMED` on the surefire `argLine`.
+Without it, `testSameBeanAcrossMappersReusesSameMutatorClass` fails with two
+distinct `Class<?>` instances carrying identical fully-qualified names — the
+exact fingerprint of the leak. This is **not a test-environment quirk**; it
+affects every real Afterburner user on Java 9+. See issue #348 for the fix
+plan.
+
+## References
+
+- PR #347: rationale for the module's structure and initial coverage
+- Issue #348: afterburner classloader caching regression (surfaced here)

afterburner-tests/pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>tools.jackson.module</groupId>
+    <artifactId>jackson-modules-base</artifactId>
+    <version>3.2.0-SNAPSHOT</version>
+  </parent>
+
+  <artifactId>jackson-module-afterburner-tests</artifactId>
+  <name>Jackson module: Afterburner integration tests</name>
+  <packaging>jar</packaging>
+
+  <description>Classpath-mode integration tests for jackson-module-afterburner. This module
+intentionally has no module-info.java so that its test POJOs live in the unnamed module, where
+their packages are not sealed-by-module. That lets Afterburner exercise its bytecode injection
+paths (PropertyMutatorCollector, CreatorOptimizer, PropertyAccessorCollector) — paths that are
+gated off when the target bean sits in a named JPMS module. This module is test-only and is
+never published.</description>
+
+  <dependencies>
+    <dependency>
+      <groupId>tools.jackson.module</groupId>
+      <artifactId>jackson-module-afterburner</artifactId>
+      <version>${project.version}</version>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <!-- This module is test-only and must never produce a publishable artifact.
+           Packaging stays `jar` so the compile + test lifecycle runs normally,
+           but every artifact-producing / artifact-publishing plugin inherited
+           from the parent chain is unbound here.
+
+           Verified via `mvn help:effective-pom -pl afterburner-tests`: every
+           execution listed below appears in the merged model at phase=none or
+           with skip=true. If you rename an execution here, re-verify with that
+           command — a typo turns into silent dead config and stale artifacts
+           in target/ rather than a build error. -->
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-jar-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>default-jar</id>
+            <phase>none</phase>
+          </execution>
+        </executions>
+      </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-install-plugin</artifactId>
+        <configuration>
+          <skip>true</skip>
+        </configuration>
+      </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-deploy-plugin</artifactId>
+        <configuration>
+          <skip>true</skip>
+        </configuration>
+      </plugin>
+      <!-- Felix bundle plugin: the parent POM binds two explicit executions
+           (`bundle-manifest` and `default-install`) so we override both by id. -->
+      <plugin>
+        <groupId>org.apache.felix</groupId>
+        <artifactId>maven-bundle-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>bundle-manifest</id>
+            <phase>none</phase>
+          </execution>
+          <execution>
+            <id>default-install</id>
+            <phase>none</phase>
+          </execution>
+        </executions>
+      </plugin>
+      <!-- CycloneDX SBOM plugin has a plugin-level `skip` flag, which disables
+           it independently of execution id merging. More robust than binding a
+           phase-override to an unnamed parent execution. -->
+      <plugin>
+        <groupId>org.cyclonedx</groupId>
+        <artifactId>cyclonedx-maven-plugin</artifactId>
+        <configuration>
+          <skip>true</skip>
+        </configuration>
+      </plugin>
+      <!-- Gradle module metadata plugin has no `skip` parameter, so we unbind
+           the parent's unnamed execution via id-based merge. Maven treats
+           `default` as the id for unnamed executions when merging child POM
+           overrides. Verified in the effective POM. -->
+      <plugin>
+        <groupId>org.gradlex</groupId>
+        <artifactId>gradle-module-metadata-maven-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>default</id>
+            <phase>none</phase>
+          </execution>
+        </executions>
+      </plugin>
+      <!-- Jacoco report analyzes 0 classes in this module (no main sources) and
+           only produces log noise. Unbind the `report` execution. Leave
+           `prepare-agent` alone: it is silent and sets the surefire agent which
+           is harmless even when no main classes exist. -->
+      <plugin>
+        <groupId>org.jacoco</groupId>
+        <artifactId>jacoco-maven-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>report</id>
+            <phase>none</phase>
+          </execution>
+        </executions>
+      </plugin>
+      <!-- Force surefire to classpath mode: this module has no module-info.java,
+           so tests must run on the classpath (unnamed module) to keep test POJO
+           packages unsealed.
+
+           The add-opens flag below is required by Afterburner itself, not by
+           the tests. Afterburner's MyClassLoader reflectively invokes
+           ClassLoader#findLoadedClass and ClassLoader#defineClass on the bean's
+           parent classloader so that generated mutator classes are cached on
+           that parent and reused across mappers. Both methods live in
+           java.base/java.lang and on Java 17+ are only reachable when the
+           module is opened to the unnamed module. Without this flag,
+           Afterburner silently falls back to defining each generated class in
+           a fresh throwaway MyClassLoader, which leaks classloaders under load
+           (and which GeneratedClassCachingTest catches as a regression).
+
+           Note: reflection into databind internals from the tests themselves
+           works without opens because this module runs on the classpath, where
+           setAccessible(true) from the unnamed module is unrestricted.
+
+           Note 2: surefire's argLine is additive when jacoco's prepare-agent
+           already set a value, so we reference @{argLine} to preserve the
+           jacoco agent config. -->
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-surefire-plugin</artifactId>
+        <configuration>
+          <useModulePath>false</useModulePath>
+          <argLine>@{argLine} --add-opens java.base/java.lang=ALL-UNNAMED</argLine>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>