Pasted

import junit.framework.TestCase;
 
import java.io.ByteArrayOutputStream;
import java.io.PrintStream;
 
public class NumberOfBottlesOfBeerOnTheWallTest extends TestCase {
 
    private static final String NL = System.lineSeparator();
 
    public void testZeroBottlesOfBeerOnTheWall() {
        final String actualOutput = captureStandardOutput(() -> NumberOfBottlesOfBeerOnTheWall.singNumberOfBottlesOfBeerOnTheWall(0));
 
        assertEquals(
                "No bottles of beer" + " on the wall. "
                        + "No bottles of beer. "
                        + "There are no more to pass around. "
                        + "No bottles of beer" + " on the wall." + NL,
                actualOutput);
    }
 
    public void testOneBottleOfBeerOnTheWall() {
        final String actualOutput = captureStandardOutput(() -> NumberOfBottlesOfBeerOnTheWall.singNumberOfBottlesOfBeerOnTheWall(1));
 
        assertEquals(
                "1 bottle of beer on the wall. "
                        + "1 bottle of beer. "
                        + "Take it down and pass it around. "
                        + "No bottles of beer" + " on the wall." + NL
                        //
                        + "No bottles of beer" + " on the wall. "
                        + "No bottles of beer. "
                        + "There are no more to pass around. "
                        + "No bottles of beer" + " on the wall." + NL,
                actualOutput);
    }
 
    public void testTwoBottleOfBeerOnTheWall() {
        final String actualOutput = captureStandardOutput(() -> NumberOfBottlesOfBeerOnTheWall.singNumberOfBottlesOfBeerOnTheWall(2));
 
        assertEquals(
                "2 bottles of beer" + " on the wall. "
                        + "2 bottles of beer. "
                        + "Take one down and pass it around. "
                        + "1 bottle of beer on the wall." + NL
                        //
                        + "1 bottle of beer on the wall. "
                        + "1 bottle of beer. "
                        + "Take it down and pass it around. "
                        + "No bottles of beer" + " on the wall." + NL
                        //
                        + "No bottles of beer" + " on the wall. "
                        + "No bottles of beer. "
                        + "There are no more to pass around. "
                        + "No bottles of beer" + " on the wall." + NL,
                actualOutput);
    }
 
    public void testThreeBottleOfBeerOnTheWall() {
        final String actualOutput = captureStandardOutput(() -> NumberOfBottlesOfBeerOnTheWall.singNumberOfBottlesOfBeerOnTheWall(3));
 
        assertEquals(
                "3 bottles of beer on the wall. "
                        + "3 bottles of beer. "
                        + "Take one down and pass it around. "
                        + "2 bottles of beer on the wall." + NL
                        //
                        + "2 bottles of beer" + " on the wall. "
                        + "2 bottles of beer. "
                        + "Take one down and pass it around. "
                        + "1 bottle of beer on the wall." + NL
                        //
                        + "1 bottle of beer on the wall. "
                        + "1 bottle of beer. "
                        + "Take it down and pass it around. "
                        + "No bottles of beer" + " on the wall." + NL
                        //
                        + "No bottles of beer" + " on the wall. "
                        + "No bottles of beer. "
                        + "There are no more to pass around. "
                        + "No bottles of beer" + " on the wall." + NL,
                actualOutput);
    }
 
    private String captureStandardOutput(final Runnable callback) {
        final PrintStream oldSystemOut = System.out;
        final ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        final PrintStream printStream = new PrintStream(byteArrayOutputStream);
        System.setOut(printStream);
        try {
            callback.run();
        } finally {
            System.setOut(oldSystemOut);
            printStream.close();
        }
 
        return byteArrayOutputStream.toString();
    }
 
}