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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.commons.math4.legacy.stat.descriptive;
  
  import org.apache.commons.math4.legacy.TestUtils;
  import org.apache.commons.math4.legacy.stat.descriptive.moment.SecondMoment;
  import org.apache.commons.math4.core.jdkmath.JdkMath;
  import org.junit.Assert;
  import org.junit.Test;
  
  /**
   * Test cases for {@link StorelessUnivariateStatistic} classes.
   */
  public abstract class StorelessUnivariateStatisticAbstractTest
      extends UnivariateStatisticAbstractTest {
  
      /** Small sample arrays */
      protected double[][] smallSamples = {{}, {1}, {1,2}, {1,2,3}, {1,2,3,4}};
  
      /** Return a new instance of the statistic */
      @Override
      public abstract UnivariateStatistic getUnivariateStatistic();
  
      /**Expected value for  the testArray defined in UnivariateStatisticAbstractTest */
      @Override
      public abstract double expectedValue();
  
      /**
       *  Verifies that increment() and incrementAll work properly.
       */
      @Test
      public void testIncrementation() {
  
          StorelessUnivariateStatistic statistic =
              (StorelessUnivariateStatistic) getUnivariateStatistic();
  
          // Add testArray one value at a time and check result
          for (int i = 0; i < testArray.length; i++) {
              statistic.increment(testArray[i]);
          }
  
          Assert.assertEquals(expectedValue(), statistic.getResult(), getTolerance());
          Assert.assertEquals(testArray.length, statistic.getN());
  
          statistic.clear();
  
          // Add testArray all at once and check again
          statistic.incrementAll(testArray);
          Assert.assertEquals(expectedValue(), statistic.getResult(), getTolerance());
          Assert.assertEquals(testArray.length, statistic.getN());
  
          statistic.clear();
  
          // Cleared
          checkClearValue(statistic);
          Assert.assertEquals(0, statistic.getN());
      }
  
      protected void checkClearValue(StorelessUnivariateStatistic statistic){
          Assert.assertTrue(Double.isNaN(statistic.getResult()));
      }
  
      @Test
      public void testEqualsAndHashCode() {
          StorelessUnivariateStatistic statistic =
              (StorelessUnivariateStatistic) getUnivariateStatistic();
          StorelessUnivariateStatistic statistic2 = null;
  
          Assert.assertFalse("non-null, compared to null", statistic.equals(statistic2));
          Assert.assertEquals("reflexive, non-null", statistic, statistic);
  
          int emptyHash = statistic.hashCode();
          statistic2 = (StorelessUnivariateStatistic) getUnivariateStatistic();
          Assert.assertEquals("empty stats should be equal", statistic, statistic2);
          Assert.assertEquals("empty stats should have the same hash code",
                  emptyHash, statistic2.hashCode());
  
          statistic.increment(1d);
          Assert.assertEquals("reflexive, non-empty", statistic, statistic);
          Assert.assertNotEquals("non-empty, compared to empty", statistic, statistic2);
          Assert.assertNotEquals("non-empty, compared to empty", statistic2, statistic);
          Assert.assertTrue("non-empty stat should have different hash code from empty stat",
                  statistic.hashCode() != emptyHash);
  
          statistic2.increment(1d);
         Assert.assertEquals("stats with same data should be equal", statistic, statistic2);
         Assert.assertEquals("stats with same data should have the same hash code",
                 statistic.hashCode(), statistic2.hashCode());
 
         statistic.increment(Double.POSITIVE_INFINITY);
         Assert.assertNotEquals("stats with different n's should not be equal", statistic2, statistic);
         Assert.assertTrue("stats with different n's should have different hash codes",
                 statistic.hashCode() != statistic2.hashCode());
 
         statistic2.increment(Double.POSITIVE_INFINITY);
         Assert.assertEquals("stats with same data should be equal", statistic, statistic2);
         Assert.assertEquals("stats with same data should have the same hash code",
                 statistic.hashCode(), statistic2.hashCode());
 
         statistic.clear();
         statistic2.clear();
         Assert.assertEquals("cleared stats should be equal", statistic, statistic2);
         Assert.assertEquals("cleared stats should have thash code of empty stat",
                 emptyHash, statistic2.hashCode());
         Assert.assertEquals("cleared stats should have thash code of empty stat",
                 emptyHash, statistic.hashCode());
     }
 
     @Test
     public void testMomentSmallSamples() {
         UnivariateStatistic stat = getUnivariateStatistic();
         if (stat instanceof SecondMoment) {
             SecondMoment moment = (SecondMoment) getUnivariateStatistic();
             Assert.assertTrue(Double.isNaN(moment.getResult()));
             moment.increment(1d);
             Assert.assertEquals(0d, moment.getResult(), 0);
         }
     }
 
     /**
      * Make sure that evaluate(double[]) and inrementAll(double[]),
      * getResult() give same results.
      */
     @Test
     public void testConsistency() {
         StorelessUnivariateStatistic stat = (StorelessUnivariateStatistic) getUnivariateStatistic();
         stat.incrementAll(testArray);
         Assert.assertEquals(stat.getResult(), stat.evaluate(testArray), getTolerance());
         for (int i = 0; i < smallSamples.length; i++) {
             stat.clear();
             for (int j =0; j < smallSamples[i].length; j++) {
                 stat.increment(smallSamples[i][j]);
             }
             TestUtils.assertEquals(stat.getResult(), stat.evaluate(smallSamples[i]), getTolerance());
         }
     }
 
     /**
      * Verifies that copied statistics remain equal to originals when
      * incremented the same way.
      */
     @Test
     public void testCopyConsistency() {
 
         StorelessUnivariateStatistic master =
             (StorelessUnivariateStatistic) getUnivariateStatistic();
 
         StorelessUnivariateStatistic replica = null;
 
         // Randomly select a portion of testArray to load first
         long index = JdkMath.round((JdkMath.random()) * testArray.length);
 
         // Put first half in master and copy master to replica
         master.incrementAll(testArray, 0, (int) index);
         replica = master.copy();
 
         // Check same
         Assert.assertEquals(replica, master);
         Assert.assertEquals(master, replica);
 
         // Now add second part to both and check again
         master.incrementAll(testArray,
                 (int) index, (int) (testArray.length - index));
         replica.incrementAll(testArray,
                 (int) index, (int) (testArray.length - index));
         Assert.assertEquals(replica, master);
         Assert.assertEquals(master, replica);
     }
 
     /**
      * Make sure that evaluate(double[]) does not alter the internal state.
      */
     @Test
     public void testEvaluateInternalState() {
         StorelessUnivariateStatistic stat = (StorelessUnivariateStatistic) getUnivariateStatistic();
         stat.evaluate(testArray);
         Assert.assertEquals(0, stat.getN());
 
         stat.incrementAll(testArray);
 
         StorelessUnivariateStatistic savedStatistic = stat.copy();
 
         Assert.assertNotEquals(stat.getResult(), stat.evaluate(testArray, 0, 5), getTolerance());
 
         Assert.assertEquals(savedStatistic.getResult(), stat.getResult(), 0.0);
         Assert.assertEquals(savedStatistic.getN(), stat.getN());
     }
 }