server/testing/src/test/java/org/apache/james/utils/DiscreteDistributionTest.java

/****************************************************************
 * 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.james.utils;

import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.assertThatThrownBy;

import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

import org.apache.james.utils.DiscreteDistribution.DistributionEntry;
import org.assertj.core.data.Offset;
import org.junit.jupiter.api.Test;

import com.google.common.collect.ImmutableList;

class DiscreteDistributionTest {
    public static final Offset<Long> OFFSET = Offset.offset(10_000L);

    @Test
    void createShouldNotSupportNegativeDistribution() {
        assertThatThrownBy(() -> new DistributionEntry<>("a", -1))
            .isInstanceOf(IllegalArgumentException.class);
    }

    @Test
    void createShouldSupportZeroDistribution() {
        DiscreteDistribution<String> testee = DiscreteDistribution.create(
            ImmutableList.of(
                new DistributionEntry<>("a", 0),
                new DistributionEntry<>("b", 1)));

        assertThat(testee.generateRandomStream().limit(10)).containsOnly("b");
    }

    @Test
    void createShouldNotSupportEmptyDistribution() {
        assertThatThrownBy(() -> DiscreteDistribution.create(ImmutableList.of()))
            .isInstanceOf(IllegalArgumentException.class);
    }

    @Test
    void createShouldNotSupportEffectivelyEmptyDistribution() {
        assertThatThrownBy(() -> DiscreteDistribution.create(
            ImmutableList.of(
                new DistributionEntry<>("a", 0),
                new DistributionEntry<>("b", 0))))
            .isInstanceOf(IllegalArgumentException.class);
    }


    @Test
    void streamOfSingleDistributionMapShouldAlwaysReturnSameElement() {
        DiscreteDistribution<String> testee = DiscreteDistribution.create(
            ImmutableList.of(
                new DistributionEntry<>("a", 1)));

        assertThat(testee.generateRandomStream().limit(10)).containsOnly("a");
    }

    @Test
    void streamOfEvenDistributionMapShouldReturnSameNumberOfEachElement() {
        DiscreteDistribution<String> testee = DiscreteDistribution.create(
            ImmutableList.of(
                new DistributionEntry<>("a", 10),
                new DistributionEntry<>("b", 10)));

        Map<String, Long> experimentOutcome = testee.generateRandomStream().limit(1_000_000)
            .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
        assertThat(experimentOutcome.get("a"))
            .isCloseTo(experimentOutcome.get("b"), OFFSET);
    }

    @Test
    void streamOfSpecificDistributionMapShouldReturnTwiceMoreA() {
        DiscreteDistribution<String> testee = DiscreteDistribution.create(
            ImmutableList.of(
                new DistributionEntry<>("a", 20),
                new DistributionEntry<>("b", 10)));

        Map<String, Long> experimentOutcome = testee.generateRandomStream().limit(1_000_000)
            .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
        assertThat(experimentOutcome.get("a"))
            .isCloseTo(experimentOutcome.get("b") * 2, OFFSET);
    }

    @Test
    void partitionShouldSupportDuplicatedDistributionEntry() {
        DiscreteDistribution<String> testee = DiscreteDistribution.create(
            ImmutableList.of(
                new DistributionEntry<>("a", 10),
                new DistributionEntry<>("b", 10),
                new DistributionEntry<>("a", 10)));

        Map<String, Long> experimentOutcome = testee.generateRandomStream().limit(1_000_000)
            .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
        assertThat(experimentOutcome.get("a"))
            .isCloseTo(experimentOutcome.get("b") * 2, OFFSET);
    }

}