commons-numbers-primes/src/test/java/org/apache/commons/numbers/primes/PrimesTest.java

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 * 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
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 *      http://www.apache.org/licenses/LICENSE-2.0
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 * distributed under the License is distributed on an "AS IS" BASIS,
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package org.apache.commons.numbers.primes;


import java.text.MessageFormat;
import java.util.HashSet;
import java.util.List;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

public class PrimesTest {

    public static final int[] PRIMES = {//primes here have been verified one by one using Dario Alejandro Alpern's tool, see http://www.alpertron.com.ar/ECM.HTM
            2,3,5,7,11,13,17,19,23,29,31,43,47,53,71,73,79,89,97,
            107,137,151,157,271,293,331,409,607,617,683,829,
            1049,1103,1229,1657,
            2039,2053,//around first boundary in miller-rabin
            2251,2389,2473,2699,3271,3389,3449,5653,6449,6869,9067,9091,
            11251,12433,12959,22961,41047,46337,65413,80803,91577,92693,
            118423,656519,795659,
            1373639,1373677,//around second boundary in miller-rabin
            588977,952381,
            1013041,1205999,2814001,
            22605091,
            25325981,25326023,//around third boundary in miller-rabin
            100000007,715827881,
            2147483647//Integer.MAX_VALUE
            };

    public static final int[] NOT_PRIMES = {//composite chosen at random + particular values used in algorithms such as boundaries for millerRabin
            4,6,8,9,10,12,14,15,16,18,20,21,22,24,25,
            275,
            2037,2041,2045,2046,2047,2048,2049,2051,2055,//around first boundary in miller-rabin
            9095,
            463465,
            1373637,1373641,1373651,1373652,1373653,1373654,1373655,1373673,1373675,1373679,//around second boundary in miller-rabin
            25325979,25325983,25325993,25325997,25325999,25326001,25326003,25326007,25326009,25326011,25326021,25326025,//around third boundary in miller-rabin
            100000005,
            1073741341,1073741823,2147473649,2147483641,2147483643,2147483645,2147483646};

    public static final int[] BELOW_2 = {
            Integer.MIN_VALUE,-1,0,1};

    void assertPrimeFactorsException(int n, String expected) {
        try {
            Primes.primeFactors(n);
            Assertions.fail("Exception not thrown");
        } catch (IllegalArgumentException e) {
            Assertions.assertEquals(expected, e.getMessage());
        }
    }
    void assertNextPrimeException(int n, String expected){
        try {
            Primes.nextPrime(n);
            Assertions.fail("Exception not thrown");
        } catch(IllegalArgumentException e) {
            Assertions.assertEquals(expected, e.getMessage());
        }
    }

    @Test
    public void testNextPrime() {

        Assertions.assertEquals(2, Primes.nextPrime(0));
        Assertions.assertEquals(2, Primes.nextPrime(1));
        Assertions.assertEquals(2, Primes.nextPrime(2));
        Assertions.assertEquals(3, Primes.nextPrime(3));
        Assertions.assertEquals(5, Primes.nextPrime(4));
        Assertions.assertEquals(5, Primes.nextPrime(5));

        for (int i = 0; i < SmallPrimes.PRIMES.length - 1; i++) {
            for (int j = SmallPrimes.PRIMES[i] + 1; j <= SmallPrimes.PRIMES[i + 1]; j++) {
                Assertions.assertEquals(SmallPrimes.PRIMES[i+1], Primes.nextPrime(j));
            }
        }

        Assertions.assertEquals(25325981, Primes.nextPrime(25325981));
        for (int i = 25325981 + 1; i <= 25326023; i++) {
            Assertions.assertEquals(25326023, Primes.nextPrime(i));
        }

        Assertions.assertEquals(Integer.MAX_VALUE, Primes.nextPrime(Integer.MAX_VALUE - 10));
        Assertions.assertEquals(Integer.MAX_VALUE, Primes.nextPrime(Integer.MAX_VALUE - 1));
        Assertions.assertEquals(Integer.MAX_VALUE, Primes.nextPrime(Integer.MAX_VALUE));

        assertNextPrimeException(Integer.MIN_VALUE, MessageFormat.format(Primes.NUMBER_TOO_SMALL,Integer.MIN_VALUE,0));
        assertNextPrimeException(-1, MessageFormat.format(Primes.NUMBER_TOO_SMALL,-1,0));
        assertNextPrimeException(-13, MessageFormat.format(Primes.NUMBER_TOO_SMALL,-13,0));
    }

    @Test
    public void testIsPrime() throws Exception {
        for (int i : BELOW_2) {
            Assertions.assertFalse(Primes.isPrime(i));
        }
        for (int i:NOT_PRIMES) {
            Assertions.assertFalse(Primes.isPrime(i));
        }
        for (int i:PRIMES) {
            Assertions.assertTrue(Primes.isPrime(i));
        }
    }

    static int sum(List<Integer> numbers){
        int out = 0;
        for (int i:numbers) {
            out += i;
        }
        return out;
    }
    static int product(List<Integer> numbers) {
        int out = 1;
        for (int i : numbers) {
            out *= i;
        }
        return out;
    }
    static final HashSet<Integer> PRIMES_SET = new HashSet<Integer>();
    static {
        for (int p : PRIMES) {
            PRIMES_SET.add(p);
        }
    }
    static void checkPrimeFactors(List<Integer> factors){
        for (int p : factors) {
            if (!PRIMES_SET.contains(p)) {
                Assertions.fail("Not found in primes list: " + p);
            }
        }
    }

    @Test
    public void testPrimeFactors() throws Exception {
        for (int i : BELOW_2) {
            assertPrimeFactorsException(i, MessageFormat.format(Primes.NUMBER_TOO_SMALL,i,2));
        }
        for (int i : NOT_PRIMES) {
            List<Integer> factors = Primes.primeFactors(i);
            checkPrimeFactors(factors);
            int prod = product(factors);
            Assertions.assertEquals(i, prod);
        }
        for (int i : PRIMES) {
            List<Integer> factors = Primes.primeFactors(i);
            Assertions.assertEquals(i, (int)factors.get(0));
            Assertions.assertEquals(1, factors.size());
        }
    }
}