Is there a way to compare an output that returns void value in Junit?

Question

public void print_star(int star)
{
    if (star == 0) return;
    System.out.print("* ");
    print_star(star - 1);
}

When I send the value 5 to this code, it outputs "* * * * * * ". I want to write a Junit code for this, but since it returns void type, I wrote in Junit;

@Test
void printStar() {
    var printStar=new Star();
      printStar.print_star(5);
      assertEquals("* * * * * ",printStar.print_star(5));
}

this code gives an error because it cannot compare void type and String. Is there any solution to compare them?