spring-boot-rest/guava-io/src/main/test/java/com/baeldung/guava/GuavaCountingOutputStreamUnitTest.java

package org.baeldung.guava;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;

import org.junit.Test;

import com.google.common.io.CountingOutputStream;

public class GuavaCountingOutputStreamUnitTest {
    public static final int MAX = 5;

    @Test(expected = RuntimeException.class)
    public void givenData_whenCountReachesLimit_thenThrowException() throws Exception {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        CountingOutputStream cos = new CountingOutputStream(out);

        byte[] data = new byte[1024];
        ByteArrayInputStream in = new ByteArrayInputStream(data);

        int b;
        while ((b = in.read()) != -1) {
            cos.write(b);
            if (cos.getCount() >= MAX) {
                throw new RuntimeException("Write limit reached");
            }
        }
    }
}