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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.rng.sampling.distribution;
18  
19  import org.apache.commons.rng.UniformRandomProvider;
20  import org.apache.commons.rng.sampling.RandomAssert;
21  import org.apache.commons.rng.simple.RandomSource;
22  import org.junit.Assert;
23  import org.junit.Test;
24  
25  /**
26   * Test for the {@link SmallMeanPoissonSampler}. The tests hit edge cases for the sampler.
27   */
28  public class SmallMeanPoissonSamplerTest {
29      /**
30       * Test the constructor with a bad mean.
31       */
32      @Test(expected = IllegalArgumentException.class)
33      public void testConstructorThrowsWithMeanThatSetsProbabilityP0ToZero() {
34          final UniformRandomProvider rng =
35              RandomSource.create(RandomSource.SPLIT_MIX_64);
36          final double p0 = Double.MIN_VALUE;
37          // Note: p0 = Math.exp(-mean) => mean = -Math.log(p0).
38          // Add to the limit on the mean to cause p0 to be zero.
39          final double mean = -Math.log(p0) + 1;
40          SmallMeanPoissonSampler.of(rng, mean);
41      }
42  
43      /**
44       * Test the constructor with a bad mean.
45       */
46      @Test(expected = IllegalArgumentException.class)
47      public void testConstructorThrowsWithZeroMean() {
48          final UniformRandomProvider rng =
49              RandomSource.create(RandomSource.SPLIT_MIX_64);
50          final double mean = 0;
51          SmallMeanPoissonSampler.of(rng, mean);
52      }
53  
54      /**
55       * Test the sample is bounded to 1000 * mean.
56       */
57      @Test
58      public void testSampleUpperBounds() {
59          // If the nextDouble() is always 1 then the sample will hit the upper bounds
60          final UniformRandomProvider rng = new UniformRandomProvider() {
61              // CHECKSTYLE: stop all
62              public long nextLong(long n) { return 0; }
63              public long nextLong() { return 0; }
64              public int nextInt(int n) { return 0; }
65              public int nextInt() { return 0; }
66              public float nextFloat() { return 0; }
67              public double nextDouble() { return 1;}
68              public void nextBytes(byte[] bytes, int start, int len) {}
69              public void nextBytes(byte[] bytes) {}
70              public boolean nextBoolean() { return false; }
71              // CHECKSTYLE: resume all
72          };
73          for (double mean : new double[] {0.5, 1, 1.5, 2.2}) {
74              final SharedStateDiscreteSampler sampler = SmallMeanPoissonSampler.of(rng, mean);
75              final int expected = (int) Math.ceil(1000 * mean);
76              Assert.assertEquals(expected, sampler.sample());
77          }
78      }
79  
80      /**
81       * Test the SharedStateSampler implementation.
82       */
83      @Test
84      public void testSharedStateSampler() {
85          final UniformRandomProvider rng1 = RandomSource.create(RandomSource.SPLIT_MIX_64, 0L);
86          final UniformRandomProvider rng2 = RandomSource.create(RandomSource.SPLIT_MIX_64, 0L);
87          final double mean = 1.23;
88          final SharedStateDiscreteSampler sampler1 =
89              SmallMeanPoissonSampler.of(rng1, mean);
90          final SharedStateDiscreteSampler sampler2 = sampler1.withUniformRandomProvider(rng2);
91          RandomAssert.assertProduceSameSequence(sampler1, sampler2);
92      }
93  }