Catches STDOUT and writes it into a string

StdoutCatcher.java

public static String catchStdout(Runnable runnable) {
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    System.setOut(new PrintStream(outputStream));
    runnable.run();
    return outputStream.toString();
}

 @Test
 void testCatchStdout() {
    String s = "Hello, World";
    assertEquals(s + "\n", catchStdout(() -> System.out.println(s)));
 }