import junit.framework.TestCase;

import java.io.ByteArrayOutputStream;
import java.io.PrintStream;

public class HelloWorldTest extends TestCase {
    public void testHelloWorld() {
        final var oldSystemOut = System.out;
        final var outputStream = new ByteArrayOutputStream();
        System.setOut(new PrintStream(outputStream));
        try {
            HelloWorld.main(null);
        } finally {
            System.setOut(oldSystemOut);
        }
        assertEquals("Hello world!" + System.lineSeparator(), outputStream.toString());
    }
}