How do I include src/test/java files to run TestNG tests?

I'm just learning Java and could use your help. I'm using Eclipse, and created a Maven project using the org.openjfx archetype. Everything seems to work fine except when I try to write tests in src/test/java, which causes an error.

An error occurred while instantiating class starcraft.warcraft.test.TestClass: Unable to make public starcraft.warcraft.test.TestClass() accessible: module starcraft.warcraft does not "exports starcraft.warcraft.test" to module org.testng

This is how I created the project with default settings in Eclipse:

Project Setup with Maven Archetype Selection

Now, when Eclipse creates the project, it doesn't have a src/test/java folder, so I create that manually. Then I create a class called "TestClass" inside a package "starcraft.warcraft.test" inside src/test/java, and I add a simple method to test inside the App class called "adder". You can see the project structure

Project Structure

package starcraft.warcraft;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
public class App extends Application {

    @Override
    public void start(Stage stage) {
        var javaVersion = SystemInfo.javaVersion();
        var javafxVersion = SystemInfo.javafxVersion();

        var label = new Label("Hello, JavaFX " + javafxVersion + ", running on Java " + javaVersion + ".");
        var scene = new Scene(new StackPane(label), 640, 480);
        stage.setScene(scene);
        stage.show();
    }
    
    // WILL TEST THIS METHOD
    public static int adder(int digit1, int digit2) {
        return digit1 + digit2;
    }
    
    public static void main(String[] args) {
        launch();
    }

}

Now I want to use TestNG for the tests, and so I include it in my POM which is

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>starcraft</groupId>
    <artifactId>warcraft</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.openjfx</groupId>
            <artifactId>javafx-controls</artifactId>
            <version>13</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.testng/testng -->
        <dependency>
            <groupId>org.testng</groupId>
            <artifactId>testng</artifactId>
            <version>7.5</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.0</version>
                <configuration>
                    <release>11</release>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.openjfx</groupId>
                <artifactId>javafx-maven-plugin</artifactId>
                <version>0.0.6</version>
                <executions>
                    <execution>
                        <!-- Default configuration for running -->
                        <!-- Usage: mvn clean javafx:run -->
                        <id>default-cli</id>
                        <configuration>
                            <mainClass>starcraft.warcraft.App</mainClass>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

This is the default POM created by the Maven archetype except for the TestNG dependency I added. When I try to use TestNG, Eclipse makes me add it to the module path like so:

Maven saying I need to add the TestNG library

And here is my module-info:

module starcraft.warcraft {
    requires javafx.controls;
    requires org.testng;
    
    exports starcraft.warcraft;
}

OK, all good so far, but now when I try to run my test inside TestClass:

package starcraft.warcraft.test;

import org.testng.annotations.Test;

import starcraft.warcraft.App;

public class TestClass {

    @Test
    public void testAdder() {
        
        int sum = App.adder(1, 2);
        
        System.out.println(sum);
        
    }
}

I get the error, which again is

An error occurred while instantiating class starcraft.warcraft.test.TestClass: Unable to make public starcraft.warcraft.test.TestClass() accessible: module starcraft.warcraft does not "exports starcraft.warcraft.test" to module org.testng

I can't figure out how to do the export. When I try making the entry in module-info, it doesn't give me the option of adding the package in src/test/java, the only packages it allows me to choose from are in src/main/java.

I don't understand modules well. How can I get the program to let me run tests from src/test/java?