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junit/src/main/java/net/neoforged/fml/junit/JUnitService.java

@@ -8,6 +8,9 @@
 import org.junit.platform.launcher.LauncherSession;
 import org.junit.platform.launcher.LauncherSessionListener;
 
+/**
+ * A session listener for JUnit environments that will bootstrap a Minecraft (FML) environment.
+ */
 public class JUnitService implements LauncherSessionListener {
     private ClassLoader oldLoader;
     public JUnitService() {
@@ -16,12 +19,16 @@ public JUnitService() {
 
     @Override
     public void launcherSessionOpened(LauncherSession session) {
+        // When the tests are started we want to make sure that they run on the transforming class loader which is set up by
+        // bootstrapping BSL which will then load the launch target
         oldLoader = Thread.currentThread().getContextClassLoader();
         Thread.currentThread().setContextClassLoader(LaunchWrapper.getTransformingLoader());
     }
 
     @Override
     public void launcherSessionClosed(LauncherSession session) {
+        // Reset the loader in case JUnit wants to execute some pre-shutdown commands
+        // and our custom class loader might throw it off
         Thread.currentThread().setContextClassLoader(oldLoader);
     }
 }

junit/src/main/java/net/neoforged/fml/junit/LaunchWrapper.java

@@ -13,6 +13,11 @@
 public class LaunchWrapper {
     private static ClassLoader transformingCL;
 
+    /**
+     * Lazily get the transforming module class loader used by the game at runtime by loading the game when needed.
+     * <p>
+     * Since in a JUnit environment we can't easily get the launch arguments, we will load them from the file specified via the {@code fml.junit.argsfile} system property.
+     */
     public static synchronized ClassLoader getTransformingLoader() {
         if (transformingCL != null) return transformingCL;
         final var oldLoader = Thread.currentThread().getContextClassLoader();

loader/src/main/java/net/neoforged/fml/loading/targets/JUnitDevLaunchTarget.java

@@ -7,6 +7,9 @@
 
 import net.neoforged.api.distmarker.Dist;
 
+/**
+ * A launch target for bootstrapping a slim Minecraft environment in forgedev, to be used in JUnit tests.
+ */
 public class JUnitDevLaunchTarget extends CommonDevLaunchHandler {
     @Override
     public Dist getDist() {

loader/src/main/java/net/neoforged/fml/loading/targets/JUnitUserDevLaunchTarget.java

@@ -7,6 +7,9 @@
 
 import net.neoforged.api.distmarker.Dist;
 
+/**
+ * A launch target for bootstrapping a slim Minecraft environment in userdev, to be used in JUnit tests.
+ */
 public class JUnitUserDevLaunchTarget extends ForgeUserdevLaunchHandler {
     @Override
     public Dist getDist() {