Dynamically create the RealJenkinsRuleInit plugin

src/main/java/org/jvnet/hudson/test/PluginUtils.java

@@ -42,26 +42,27 @@ static File createRealJenkinsRulePlugin(File destinationDirectory, String baseli
 
         // we need to create a jar for the classes which we can then put into the plugin.
         Path tmpClassesJar = Files.createTempFile("rjr", "jar");
-        try (FileOutputStream fos = new FileOutputStream(tmpClassesJar.toFile());
-                JarOutputStream classesJarOS = new JarOutputStream(fos, mf)) {
-
-            // the actual class
-            try (InputStream classIS = RealJenkinsRuleInit.class.getResourceAsStream(RealJenkinsRuleInit.class.getSimpleName() + ".class")) {
-                String path = RealJenkinsRuleInit.class.getPackageName().replace('.', '/');
-                createJarEntry(classesJarOS, path + '/' + RealJenkinsRuleInit.class.getSimpleName() + ".class", classIS);
+        try {
+            try (FileOutputStream fos = new FileOutputStream(tmpClassesJar.toFile());
+                    JarOutputStream classesJarOS = new JarOutputStream(fos, mf)) {
+                // the actual class
+                try (InputStream classIS = RealJenkinsRuleInit.class.getResourceAsStream(RealJenkinsRuleInit.class.getSimpleName() + ".class")) {
+                    String path = RealJenkinsRuleInit.class.getPackageName().replace('.', '/');
+                    createJarEntry(classesJarOS, path + '/' + RealJenkinsRuleInit.class.getSimpleName() + ".class", classIS);
+                }
             }
-            createJarEntry(classesJarOS, "META-INF/services/hudson.Plugin", RealJenkinsRuleInit.class.getName().getBytes(StandardCharsets.UTF_8));
-        }
 
-        // the actual JPI
-        File jpi = new File(destinationDirectory, pluginName+".jpi");
-        try (FileOutputStream fos = new FileOutputStream(jpi); JarOutputStream jos = new JarOutputStream(fos, mf)) {
-            try (FileInputStream fis = new FileInputStream(tmpClassesJar.toFile())) {
-                createJarEntry(jos, "WEB-INF/lib/"+pluginName+".jar", fis);
+            // the actual JPI
+            File jpi = new File(destinationDirectory, pluginName+".jpi");
+            try (FileOutputStream fos = new FileOutputStream(jpi); JarOutputStream jos = new JarOutputStream(fos, mf)) {
+                try (FileInputStream fis = new FileInputStream(tmpClassesJar.toFile())) {
+                    createJarEntry(jos, "WEB-INF/lib/" + pluginName + ".jar", fis);
+                }
             }
+            return jpi;
+        } finally {
+            Files.delete(tmpClassesJar);
         }
-        Files.delete(tmpClassesJar);
-        return jpi;
     }
 
     private static void createJarEntry(JarOutputStream jos, String entryName, InputStream data) throws IOException {
@@ -71,11 +72,4 @@ private static void createJarEntry(JarOutputStream jos, String entryName, InputS
         jos.closeEntry();
     }
 
-    private static void createJarEntry(JarOutputStream jos, String entryName, byte[] data) throws IOException {
-        JarEntry je = new JarEntry(entryName);
-        jos.putNextEntry(je);
-        jos.write(data);
-        jos.closeEntry();
-    }
-
 }

src/main/java/org/jvnet/hudson/test/RealJenkinsRuleInit.java

@@ -27,16 +27,27 @@
 import hudson.Plugin;
 import java.net.URL;
 import java.net.URLClassLoader;
+
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.NoExternalUse;
+
 import jenkins.model.Jenkins;
 
+/**
+ * Plugin for use by {@link RealJenkinsRule}.
+ * <p>
+ * <stong>NOTE</strong>: this and only this class is added into a dynamically generated plugin, see {@link PluginUtils#createRealJenkinsRulePlugin(java.io.File, String)}.
+ * In order for this to occur correctly there need to be no inner classes or other code dependencies here (except what can be loaded by reflection).
+ */
+@Restricted(NoExternalUse.class)
 public class RealJenkinsRuleInit extends Plugin {
 
     @SuppressWarnings("deprecation") // @Initializer just gets run too late, even with before = InitMilestone.PLUGINS_PREPARED
     public RealJenkinsRuleInit() {}
 
     @Override
     public void start() throws Exception {
-        new URLClassLoader(new URL[] {new URL(System.getProperty("RealJenkinsRule.location"))}, ClassLoader.getSystemClassLoader().getParent()).
+        new URLClassLoader("RealJenkinsRule",new URL[] {new URL(System.getProperty("RealJenkinsRule.location"))}, ClassLoader.getSystemClassLoader().getParent()).
                 loadClass("org.jvnet.hudson.test.RealJenkinsRule$Init2").
                 getMethod("run", Object.class).
                 invoke(null, Jenkins.get());

src/test/java/org/jvnet/hudson/test/RealJenkinsRuleTest.java

@@ -361,7 +361,7 @@ private static void hangs(JenkinsRule r) throws Throwable {
 
     @Test
     public void noDetachedPlugins() throws Throwable {
-        // XXX this test will falsely pass if the RealJenkinsRuleInit plugin targets a version of Jenkins that has no detacthed plugins.
+        // we should be the only plugin in Jenkins.
         rr.then(RealJenkinsRuleTest::_noDetachedPlugins);
     }