SampleStatisticTest.java

package org.eclipse.jetty.util.statistic;

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

import org.junit.Test;


/* ------------------------------------------------------------ */
public class SampleStatisticTest
{
    private static long[][] data = 
    {
        {100,100,100,100,100,100,100,100,100,100},
        {100,100,100,100,100,100,100,100,100,100,90,110},
        {100,100,100,100,100,100,100,100,90,110,95,105,97,103},
        {100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,90,110,95,105,97,103},
    };
    
    private static double[][] results =
    { /* {mean,stddev}*/
        {100.0,0.0},
        {100.0,Math.sqrt((10*10+10*10)/12.0)},
        {100.0,Math.sqrt((10*10+10*10+5*5+5*5+3*3+3*3)/14.0)},
        {100.0,Math.sqrt((10*10+10*10+5*5+5*5+3*3+3*3)/24.0)},
        {100.0,Math.sqrt((10*10+10*10+5*5+5*5+3*3+3*3)/104.0)}
    };
    
    
    @Test
    public void testData()
        throws Exception
    {
        SampleStatistic stats = new SampleStatistic();
        for (int d=0;d<data.length;d++)
        {
            stats.reset();
            for (long x : data[d])
                stats.set(x);

            assertEquals("count"+d,data[d].length, (int)stats.getCount());
            assertNearEnough("mean"+d,results[d][0], stats.getMean());
            assertNearEnough("stddev"+d,results[d][1], stats.getStdDev());
        }
    }

    private void assertNearEnough(String test,double expected, double actual)
    {
        double diff = Math.abs(expected-actual);
        if (diff<0.1)
        {
            System.out.println("Near enough "+test+" diff="+diff);
            return;
        }
        String failed = "Not near enough "+test+" expected="+expected+" actual="+actual+" diff="+diff;
        System.err.println(failed);
        assertTrue(failed,false);
    }
    
}