Add capability to only fail when running tests.

src/core/lombok/core/handlers/HandlerUtil.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2013-2025 The Project Lombok Authors.
+ * Copyright (C) 2013-2026 The Project Lombok Authors.
  * 
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -27,6 +27,7 @@ import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -57,6 +58,9 @@ import lombok.experimental.FieldDefaults;
  * target platform (e.g. useful for both javac and Eclipse lombok implementations).
  */
 public class HandlerUtil {
+	
+	private static AtomicInteger inTest = new AtomicInteger();
+	
 	private HandlerUtil() {}
 	
 	public enum FieldAccess {
@@ -1051,4 +1055,16 @@ public class HandlerUtil {
 		}
 		return null;
 	}
+	
+	public static void failIfRunningInTest(String message) throws AssertionError {
+		if (inTest.intValue() != 0) throw new AssertionError("In test: " + message);
+	}
+	
+	public static void incrementRunningInTest() {
+		inTest.incrementAndGet();
+	}
+	
+	public static void decrementRunningInTest() {
+		if (inTest.decrementAndGet() < 0) throw new IllegalStateException();
+	}
 }

test/core/src/lombok/DirectoryRunner.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2009-2024 The Project Lombok Authors.
+ * Copyright (C) 2009-2026 The Project Lombok Authors.
  * 
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -34,6 +34,7 @@ import org.junit.runner.Runner;
 import org.junit.runner.notification.Failure;
 import org.junit.runner.notification.RunNotifier;
 
+import lombok.core.handlers.HandlerUtil;
 import lombok.eclipse.Eclipse;
 import lombok.javac.Javac;
 
@@ -170,9 +171,12 @@ public class DirectoryRunner extends Runner {
 			
 			notifier.fireTestStarted(testDescription);
 			try {
+				HandlerUtil.incrementRunningInTest();
 				tester.runTest();
 			} catch (Throwable t) {
 				notifier.fireTestFailure(new Failure(testDescription, t));
+			} finally {
+				HandlerUtil.decrementRunningInTest();
 			}
 			notifier.fireTestFinished(testDescription);
 		}