curator-master/curator-x-discovery/src/test/java/org/apache/curator/x/discovery/TestStrategies.java
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 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.curator.x.discovery;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertTrue;
import com.google.common.collect.Lists;
import java.util.List;
import org.apache.commons.math.stat.descriptive.SummaryStatistics;
import org.apache.curator.x.discovery.details.InstanceProvider;
import org.apache.curator.x.discovery.strategies.RandomStrategy;
import org.apache.curator.x.discovery.strategies.RoundRobinStrategy;
import org.apache.curator.x.discovery.strategies.StickyStrategy;
import org.junit.jupiter.api.Test;

public class TestStrategies {
    private static class TestInstanceProvider implements InstanceProvider<Void> {
        private final List<ServiceInstance<Void>> instances;

        private TestInstanceProvider(int qty) throws Exception {
            this(qty, 0);
        }

        private TestInstanceProvider(int qty, int startingAt) throws Exception {
            instances = Lists.newArrayList();
            for (int i = 0; i < qty; ++i) {
                ServiceInstanceBuilder<Void> builder = ServiceInstance.builder();
                instances.add(
                        builder.id(Integer.toString(i + startingAt)).name("foo").build());
            }
        }

        @Override
        public List<ServiceInstance<Void>> getInstances() throws Exception {
            return instances;
        }
    }

    @Test
    public void testRandom() throws Exception {
        final int QTY = 10;
        final int ITERATIONS = 1000;

        TestInstanceProvider instanceProvider = new TestInstanceProvider(QTY, 0);
        ProviderStrategy<Void> strategy = new RandomStrategy<Void>();

        long[] counts = new long[QTY];
        for (int i = 0; i < ITERATIONS; ++i) {
            ServiceInstance<Void> instance = strategy.getInstance(instanceProvider);
            int id = Integer.parseInt(instance.getId());
            counts[id]++;
        }

        SummaryStatistics statistic = new SummaryStatistics();
        for (int i = 0; i < QTY; ++i) {
            statistic.addValue(counts[i]);
        }
        assertTrue(
                statistic.getStandardDeviation() <= (QTY * 2),
                "" + statistic.getStandardDeviation()); // meager check for even distribution
    }

    @Test
    public void testRoundRobin() throws Exception {
        final int QTY = 10;

        TestInstanceProvider instanceProvider = new TestInstanceProvider(QTY);
        ProviderStrategy<Void> strategy = new RoundRobinStrategy<Void>();

        for (int i = 0; i < QTY; ++i) {
            ServiceInstance<Void> instance = strategy.getInstance(instanceProvider);
            assertEquals(instance.getId(), Integer.toString(i));
        }

        for (int i = 0; i < (1234 * QTY); ++i) {
            ServiceInstance<Void> instance = strategy.getInstance(instanceProvider);
            assertEquals(instance.getId(), Integer.toString(i % QTY));
        }
    }

    @Test
    public void testSticky() throws Exception {
        final int QTY = 10;

        TestInstanceProvider instanceProvider = new TestInstanceProvider(QTY);
        StickyStrategy<Void> strategy = new StickyStrategy<Void>(new RandomStrategy<Void>());

        ServiceInstance<Void> theInstance = strategy.getInstance(instanceProvider);
        int instanceNumber = strategy.getInstanceNumber();
        for (int i = 0; i < 1000; ++i) {
            assertEquals(strategy.getInstance(instanceProvider), theInstance);
        }

        // assert what happens when an instance goes down
        instanceProvider = new TestInstanceProvider(QTY, QTY);
        assertFalse(strategy.getInstance(instanceProvider).equals(theInstance));
        assertFalse(instanceNumber == strategy.getInstanceNumber());

        theInstance = strategy.getInstance(instanceProvider);
        for (int i = 0; i < 1000; ++i) {
            assertEquals(strategy.getInstance(instanceProvider), theInstance);
        }
    }
}
