doc/testing.html

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  <code>java.util.concurrent.ThreadFactory</code>. One such implementation
  class, named Virtual, is currently part of the JDK build in the
  <code>test/jtreg_test_thread_factory/</code> directory. This class gets
  compiled during the test image build. The implementation of the Virtual
  class creates a new virtual thread for executing each test class.</p>
+ <h4 id="value_class_plugin">VALUE_CLASS_PLUGIN</h4>
+ <p>Enables the <code>ValueClassPlugin</code> javac plugin when compiling
+ and running JTReg tests. This is a <strong>temporary mode</strong>
+ intended for use while value classes (JEP 401) are a preview feature.
+ The long-term plan is to replace classes annotated with
+ <code>@jdk.test.lib.valueclass.AsValueClass</code> with plain
+ <code>value class</code> declarations once value classes are
+ finalized.</p>
+ <p>In the meantime, this mode allows test sources to compile and run as
+ either value classes or regular identity classes without source-level
+ changes.</p>
+ <p>When set to any non-empty value, the following options are appended to
+ every JTReg invocation:</p>
+ <ul>
+ <li><code>-cpa:&lt;valueClassPlugin.jar&gt;</code> — appends the plugin
+ JAR to the compile-time classpath (only when the JAR is present in the
+ test image under
+ <code>jtreg_value_class_plugin/valueClassPlugin.jar</code>).</li>
+ <li><code>-vmoption:--enable-preview</code> — enables JVM preview
+ features at runtime.</li>
+ <li><code>-javacoption:-XDaccessInternalAPI</code> — grants the compiler
+ access to internal APIs required by the plugin.</li>
+ <li><code>-javacoption:--source &lt;version&gt; --enable-preview</code>
+ — enables preview language features at compile time.</li>
+ <li><code>-javacoption:-Xplugin:ValueClassPlugin</code> — activates the
+ plugin.</li>
+ </ul>
+ <p>The plugin scans each compilation unit after parsing and converts any
+ class annotated with
+ <code>@jdk.test.lib.valueclass.AsValueClass</code> into a value class by
+ setting the internal <code>VALUE_CLASS</code> modifier flag and clearing
+ the <code>IDENTITY_TYPE</code> flag. This transformation only takes
+ effect when <code>--enable-preview</code> is active; without it the
+ annotation is a no-op and the class compiles as an ordinary identity
+ class, so the same test source can exercise both code paths.</p>
+ <p>Example:</p>
+ <pre><code>$ make test TEST=jdk_lang JTREG="VALUE_CLASS_PLUGIN=true"
+ </code></pre>
  <h4 id="jvmti_stress_agent">JVMTI_STRESS_AGENT</h4>
  <p>Executes JTReg tests with JVM TI stress agent. The stress agent is
  the part of test library and located in
  <code>test/lib/jdk/test/lib/jvmti/libJvmtiStressAgent.cpp</code>. The
  value of this argument is set as JVM TI agent options. This mode uses