Capturing stdOut and stdErr as part of a JUnit test. See https://classcube.com/junit-compare-output/ for explanations.

OutputCaptureTest.java

import java.util.*;
import java.io.*;
import static org.junit.Assert.*;
import org.junit.Test;

@SuppressWarnings( "unchecked" )
public class OutputCaptureTest {

    private final ByteArrayOutputStream outContent = new ByteArrayOutputStream();
    private final ByteArrayOutputStream errContent = new ByteArrayOutputStream();

    @Test( timeout = 250 )
    public void test() throws Exception {
      captureOut();
      
      // Run whatever code you're testing
      
      String theOutput = getOut();
      
      // Compare what you expect with theOutput

    }

    /**
     * Turns on stdOut output capture
     */
    private void captureOut() {
        System.setOut( new PrintStream( outContent ) );
    }

    /**
     * Turns on stdErr output capture
     */
    private void captureErr() {
        System.setErr( new PrintStream( errContent ) );
    }

    /**
     * Turns off stdOut capture and returns the contents
     * that have been captured
     *
     * @return
     */
    private String getOut() {
        System.setOut( new PrintStream( new FileOutputStream( FileDescriptor.out ) ) );
        return outContent.toString().replaceAll( "\r", "" );

    }

    /**
     * Turns off stdErr capture and returns the contents
     * that have been captured
     *
     * @return
     */
    private String getErr() {
        System.setErr( new PrintStream( new FileOutputStream( FileDescriptor.out ) ) );
        return errContent.toString().replaceAll( "\r", "" );
    }

}