package org.apache.logging.log4j.core.util;

import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

import org.junit.Test;

public class CyclicBufferTest {

    @Test
    public void testCyclicBuffer() {
        final CyclicBuffer<Integer> buffer = new CyclicBuffer<>(Integer.class, 3);

        assertTrue(buffer.isEmpty());
        buffer.add(1);
        assertFalse(buffer.isEmpty());
        Integer[] items = buffer.removeAll();
        assertTrue("Incorrect number of items", items.length == 1);

        assertTrue(buffer.isEmpty());
        buffer.add(1);
        buffer.add(2);
        buffer.add(3);
        buffer.add(4);
        items = buffer.removeAll();
        assertTrue("Incorrect number of items", items.length == 3);
        assertTrue(buffer.isEmpty());
    }

}

package org.apache.logging.log4j.core.util;

import static org.junit.Assert.assertArrayEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

import org.junit.Test;

public class CyclicBufferTest {

    @Test
    public void testSize0() {
        final CyclicBuffer<Integer> buffer = new CyclicBuffer<>(Integer.class, 0);

        assertTrue(buffer.isEmpty());
        buffer.add(1);
        assertTrue(buffer.isEmpty());
        Integer[] items = buffer.removeAll();
        assertTrue("Incorrect number of items", items.length == 0);

        assertTrue(buffer.isEmpty());
        buffer.add(1);
        buffer.add(2);
        buffer.add(3);
        buffer.add(4);
        items = buffer.removeAll();
        assertTrue("Incorrect number of items", items.length == 0);
        assertTrue(buffer.isEmpty());
    }

    @Test
    public void testSize1() {
        final CyclicBuffer<Integer> buffer = new CyclicBuffer<>(Integer.class, 1);

        assertTrue(buffer.isEmpty());
        buffer.add(1);
        assertFalse(buffer.isEmpty());
        Integer[] items = buffer.removeAll();
        assertTrue("Incorrect number of items", items.length == 1);

        assertTrue(buffer.isEmpty());
        buffer.add(1);
        buffer.add(2);
        buffer.add(3);
        buffer.add(4);
        items = buffer.removeAll();
        assertTrue("Incorrect number of items", items.length == 1);
        assertArrayEquals(new Integer[] { 4 }, items);
        assertTrue(buffer.isEmpty());
    }

    @Test
    public void testSize3() {
        final CyclicBuffer<Integer> buffer = new CyclicBuffer<>(Integer.class, 3);

        assertTrue(buffer.isEmpty());
        buffer.add(1);
        assertFalse(buffer.isEmpty());
        Integer[] items = buffer.removeAll();
        assertTrue("Incorrect number of items", items.length == 1);

        assertTrue(buffer.isEmpty());
        buffer.add(1);
        buffer.add(2);
        buffer.add(3);
        buffer.add(4);
        items = buffer.removeAll();
        assertTrue("Incorrect number of items", items.length == 3);
        assertArrayEquals(new Integer[] { 2, 3, 4 }, items);
        assertTrue(buffer.isEmpty());
    }

    @Test(expected = IllegalArgumentException.class)
    public void testSizeNegative() {
        final CyclicBuffer<Integer> buffer = new CyclicBuffer<>(Integer.class, -1);
    }

}

Allow for bufferSize=0 in SMTP appender. Add tests.