Add tests for underscores in pointcuts on Java 21+

See also:
https://github.com/eclipse-aspectj/eclipse.jdt.core/commit/5d2f2aecd2

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

tests/features1921/java21/UnderscoreInPointcutAspect.aj

@@ -0,0 +1,53 @@
+public aspect UnderscoreInPointcutAspect {
+  public static void main(String[] args) {
+    UnderTest u = new UnderTest();
+    System.out.println(u._add(12, 4));
+    System.out.println(u._subtract(12, 4));
+    System.out.println(u.multiply_(12, 4));
+    System.out.println(u.divide_(12, 4));
+    System.out.println(u.power_of(3, 3));
+    System.out.println(u.squareRoot(49));
+  }
+
+  before(int a, int b) : execution(* _*(..)) && args(a, b) {
+    System.out.println("[starts with underscore] " + thisJoinPoint + " -> " + a + ", " + b);
+  }
+
+  before(int a, int b) : execution(* *_(..)) && args(a, b) {
+    System.out.println("[ends with underscore] " + thisJoinPoint + " -> " + a + ", " + b);
+  }
+
+  before(int a, int b) : execution(* *_*(..)) && args(a, b) {
+    System.out.println("[contains underscore] " + thisJoinPoint + " -> " + a + ", " + b);
+  }
+
+  before(int a) : execution(* *(..)) && !execution(* *_*(..)) && args(a) {
+    System.out.println("[no underscore] " + thisJoinPoint + " -> " + a);
+  }
+}
+
+class UnderTest {
+  int _add(int a, int b) {
+    return a + b;
+  }
+
+  int _subtract(int a, int b) {
+    return a - b;
+  }
+
+  int multiply_(int a, int b) {
+    return a * b;
+  }
+
+  int divide_(int a, int b) {
+    return a / b;
+  }
+
+  int power_of(int base, int exponent) {
+    return (int) Math.pow(base, exponent);
+  }
+
+  int squareRoot(int a) {
+    return (int) Math.sqrt(a);
+  }
+}

tests/src/test/java/org/aspectj/systemtest/ajc1921/Java21PreviewFeaturesTests.java

@@ -8,6 +8,7 @@
 package org.aspectj.systemtest.ajc1921;
 
 import junit.framework.Test;
+import org.aspectj.systemtest.ajc10x.Ajc10xTests;
 import org.aspectj.testing.XMLBasedAjcTestCase;
 import org.aspectj.testing.XMLBasedAjcTestCaseForJava21Only;
 
@@ -46,6 +47,17 @@ public class Java21PreviewFeaturesTests extends XMLBasedAjcTestCaseForJava21Only
     System.out.println("Unnamed patterns still are not implemented with the Java 21 release Eclipse 2023-12 (4.30)");
   }
 
+  /**
+   * Same as {@link Ajc10xTests#test052()}, but compiled to target 21 instead of 1.4
+   */
+  public void testUnderscoreInPointcutPattern1() {
+    runTest("underscore can still be used in pointcut patterns on Java 21+ - 1");
+  }
+
+  public void testUnderscoreInPointcutPattern2() {
+    runTest("underscore can still be used in pointcut patterns on Java 21+ - 2");
+  }
+
   public void testNamedClassWithSimpleMainMethod() {
     runTest("named class with simple main method");
   }

tests/src/test/resources/org/aspectj/systemtest/ajc1921/ajc1921.xml

@@ -296,6 +296,41 @@
 		</run>
 	</ajc-test>
 
+	<!-- Java 21 preview -->
+	<ajc-test dir="new" vm="21" title="underscore can still be used in pointcut patterns on Java 21+ - 1">
+		<compile files="NotCharInPointcut.java" options="--enable-preview -21">
+			<message kind="warning" line="51" text="advice defined in A has not been applied [Xlint:adviceDidNotMatch]"/>
+			<message kind="warning" line="52" text="advice defined in A has not been applied [Xlint:adviceDidNotMatch]"/>
+			<message kind="warning" line="53" text="advice defined in A has not been applied [Xlint:adviceDidNotMatch]"/>
+		</compile>
+		<run class="NotCharInPointcut" vmargs="--enable-preview"/>
+	</ajc-test>
+
+	<!-- Java 21 preview -->
+	<ajc-test dir="features1921/java21" vm="21" title="underscore can still be used in pointcut patterns on Java 21+ - 2">
+		<compile files="UnderscoreInPointcutAspect.aj" options="--enable-preview -21"/>
+		<run class="UnderscoreInPointcutAspect" vmargs="--enable-preview">
+			<stdout>
+				<line text="[starts with underscore] execution(int UnderTest._add(int, int)) -> 12, 4"/>
+				<line text="[contains underscore] execution(int UnderTest._add(int, int)) -> 12, 4"/>
+				<line text="16"/>
+				<line text="[starts with underscore] execution(int UnderTest._subtract(int, int)) -> 12, 4"/>
+				<line text="[contains underscore] execution(int UnderTest._subtract(int, int)) -> 12, 4"/>
+				<line text="8"/>
+				<line text="[ends with underscore] execution(int UnderTest.multiply_(int, int)) -> 12, 4"/>
+				<line text="[contains underscore] execution(int UnderTest.multiply_(int, int)) -> 12, 4"/>
+				<line text="48"/>
+				<line text="[ends with underscore] execution(int UnderTest.divide_(int, int)) -> 12, 4"/>
+				<line text="[contains underscore] execution(int UnderTest.divide_(int, int)) -> 12, 4"/>
+				<line text="3"/>
+				<line text="[contains underscore] execution(int UnderTest.power_of(int, int)) -> 3, 3"/>
+				<line text="27"/>
+				<line text="[no underscore] execution(int UnderTest.squareRoot(int)) -> 49"/>
+				<line text="7"/>
+			</stdout>
+		</run>
+	</ajc-test>
+
 	<!-- Java 21 preview -->
 	<ajc-test dir="features1921/java21" vm="21" title="named class with simple main method">
 		<!-- Compiles without preview mode, but needs preview mode to run -->