Add demo test for spring-projects/spring-framework#33013 (comment)

Author: weiw005

spel-vararg/pom.xml

@@ -15,6 +15,8 @@
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <kotlin.code.style>official</kotlin.code.style>
         <kotlin.compiler.jvmTarget>1.8</kotlin.compiler.jvmTarget>
+        <maven.compiler.source>19</maven.compiler.source>
+        <maven.compiler.target>19</maven.compiler.target>
     </properties>
 
     <repositories>
@@ -100,13 +102,19 @@
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-expression</artifactId>
-            <version>6.1.8</version>
+            <version>6.1.11</version>
         </dependency>
         <dependency>
             <groupId>org.jetbrains.kotlin</groupId>
             <artifactId>kotlin-reflect</artifactId>
             <version>2.0.0</version>
         </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>3.26.3</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
 </project>

spel-vararg/src/test/java/SpelVarargArrayTest.java

@@ -0,0 +1,40 @@
+import org.junit.jupiter.api.Test;
+import org.springframework.expression.Expression;
+import org.springframework.expression.spel.standard.SpelExpressionParser;
+import org.springframework.expression.spel.support.StandardEvaluationContext;
+import org.springframework.util.ReflectionUtils;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.lang.reflect.Method;
+
+public class SpelVarargArrayTest {
+    @Test
+    public void arrayFlattenedAsVararg_Before_6_1_10() {
+        assertThat(evaluateExpression("#objectVarargDemo({'World', 123})")).isEqualTo("There are 2 argument(s): World 123");
+    }
+
+    @Test
+    public void arrayFlattenedAsVararg_After_6_1_11() {
+        assertThat(evaluateExpression("#objectVarargDemo({'World', 123})")).isEqualTo("There are 1 argument(s): [World, 123]");
+    }
+
+    private static final Method demoMethod =
+            ReflectionUtils.findMethod(SpelVarargArrayTest.class, "objectVarargDemo", Object[].class);
+
+    private static Object evaluateExpression(String expression) {
+        SpelExpressionParser parser = new SpelExpressionParser();
+        Expression exp = parser.parseExpression(expression);
+        StandardEvaluationContext context = new StandardEvaluationContext();
+        context.registerFunction("objectVarargDemo", demoMethod);
+        return exp.getValue(context);
+    }
+
+    static String objectVarargDemo(Object... args) {
+        StringBuilder sb = new StringBuilder();
+        sb.append(String.format("There are %d argument(s): ", args.length));
+        for (Object arg : args) {
+            sb.append(arg).append(" ");
+        }
+        return sb.toString().trim();
+    }
+}