A JUnit rule for testing output to `System.out`

SysoutRule.java

import static org.hamcrest.Matchers.containsString;
import static org.hamcrest.Matchers.is;
import static org.hamcrest.Matchers.not;
import static org.junit.Assert.assertThat;

public class SysoutRule implements TestRule {

    private ByteOutputStream out;

    public void contains(String string) {
        assertThat(out, not(is((ByteOutputStream) null)));
        assertThat(out.toString(), containsString(string));
    }

    @Override
    public Statement apply(Statement base, Description description) {
        return new Statement() {
            @Override
            public void evaluate() throws Throwable {
                final PrintStream oldOut = System.out;
                out = new ByteOutputStream();
                final PrintStream newOut = new PrintStream(out);
                System.setOut(newOut);
                try {
                    base.evaluate();
                } finally {
                    System.setOut(oldOut);
                    newOut.close();
                    out = null;
                }

            }
        };
    }
}

With ByteOutputStream you mean ByteArrayOutputStream?