RangeTest.java

package com.comphenix.xp;

import static org.junit.Assert.*;

import java.util.Random;

import org.junit.BeforeClass;
import org.junit.Test;

public class RangeTest {

	private static final int REPEAT_COUNT = 1000000;
	
	private static Random rnd;
	
	@BeforeClass
    public static void oneTimeSetUp() {
        // Initialize random source
		rnd = new Random();
    }
	
	@Test
	public void testRandom() {
	
		// Generate a random range
		int start = rnd.nextInt(10);
		int stop = start + 1 + rnd.nextInt(20);
		SampleRange range = new SampleRange(start, stop);
		
		int[] results = SampleValues(range, REPEAT_COUNT);
		
		double average = getAverage(results);
		double std = getStandardDeviation(average, results) / average;
		
		if (std > 0.1) {
			fail(String.format("Standard deviation (%f) is greater than 10 procent.", std));
		}
	}
	
	@Test
	public void testSpecific() {
	
		SampleRange range = new SampleRange(0.1, 0.1);
		int[] results = SampleValues(range, REPEAT_COUNT);
		
		// "0" should occur approximately 90%.
		double rate = results[0] / (double) REPEAT_COUNT;

		if (Math.abs(rate - 0.9) > 0.1)
			fail("The number 0 didn't occur 90% in the range 0 - 0.1");
	}
	
	@Test
	public void testUnbiased() {

		SampleRange range = new SampleRange(0.1, 0.5);
		int[] counts = SampleValues(range, REPEAT_COUNT);
		
		// The expected value (average)
		double expected = (range.getStart() + range.getEnd()) / 2.0;
		double average = counts[1] / (double) REPEAT_COUNT; // results[0] * 0

		if (Math.abs(expected - average) > 0.1) {
			fail("Expected value differs too much.");
		}
	}
	
	@Test
	public void testSmallRange() {

		SampleRange range = new SampleRange(0.9, 3.1);
		int[] counts = SampleValues(range, REPEAT_COUNT);
		
		double expected = 0.1 / (3.1 - 0.9);
		double actual = counts[0] / (double) REPEAT_COUNT;

		if (Math.abs(expected - actual) > 0.1) {
			fail("Small range value differs too much.");
		}
	}
	
	private int[] SampleValues(SampleRange range, int count) {
		
		int start = range.getMinimum();
		int stop = range.getMaximum();
		
		// Storage of results (stop is inclusive)
		int[] results = new int[stop - start + 1];

		for (int i = 0; i < count; i++) {
			int value = range.sampleInt(rnd);
			
			if (value >= start && value <= stop)
				results[value - start]++;
			else
				fail(String.format("Outside of range [%d, %d] with value %d", start, stop, value));
		}
		
		return results;
	}
	
	private double getAverage(int[] numbers) {
		
		double sum = 0;
		
		// Find total sum
		for (int i = 0; i < numbers.length; i++) {
			sum += numbers[i];
		}
		
		return sum / (double)numbers.length;
	}
	
	private double getStandardDeviation(double average, int[] numbers) {
		
		double sum = 0;
		
		// Sum of squares
		for (int i = 0; i < numbers.length; i++) {
			sum += (numbers[i] - average) * (numbers[i] - average);
		}
		
		return Math.sqrt(sum / numbers.length);
	}
}