Running tests with VS Code (without Maven) using the "Test Runner for Java" extension - visual-studio-code

Question

I'm trying to make a minimal working example of JUnit5 using Visual Studio code without Maven. The reason is that I'm trying to make a quick demo for 1st year students, and I don't have the time to explain Maven (it will be the subject of a later course).
My VS Code workspace has this structure (I'm on Linux so forward slashes are normal) :
The settings.json file contains:
{
"java.project.referencedLibraries": [
"demojunit/junit-platform-console-standalone-1.8.1.jar"
]
}
The DemoJUnit.java contains:
package demojunit;
import java.util.Scanner;
public class DemoJUnit {
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
int integer = -1;
do {
System.out.print("Enter an integer between 1 and 20 : ");
if (keyboard.hasNextInt())
integer = keyboard.nextInt();
keyboard.nextLine();
} while ((integer < 1) || (integer > 20));
keyboard.close();
long result = computeFactorial(integer);
System.out.println("The factorial " + integer + "! gives " + result);
}
public static long computeFactorial(int number) {
if (number < 1)
return -1;
if (number > 20)
return -2;
long factorial = 1;
for (int i = 2; i <= number; i++) {
factorial = factorial * i;
}
return factorial;
}
}
And the DemoJUnitTest.java contains:
package demojunit;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
public class DemoJUnitTest {
#Test
public static void computeFactorial_CleanTest() {
long expected_value = 120;
long real_value = DemoJUnit.computeFactorial(5);
Assertions.assertEquals(expected_value, real_value);
}
#Test public static void computeFactorial_DirtyTest() {
long expected_value = -1;
long real_value = DemoJUnit.computeFactorial(0);
Assertions.assertEquals(expected_value, real_value);
}
}
The settings.json seems to work since the imports and #Test are not marked as errors in VS Code.
As you can see in the folder image, I downloaded the latest JUnit5 jar file, and it works when running from the command line:
However, running from the command line is not convenient, so I installed the "Test Runner for Java" extension.
The problem is that when running tests, something fails and I don't have any error messages, nor any indication what went wrong. I changed the extensions' settings to be verbose but I still get no error messages in the Terminal, the Debug Console, nor anywhere else.
All I get is :
Any idea why the extension fails (and fails to give any indication on why it fails)?