gcd_test

package com.pavelperc.gcd;

import javafx.util.Pair;
import org.junit.Test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import static org.junit.Assert.*;

public class GCDTest {

    GCD gcd = new GCD();

    @Test
    public void simplest() {

        assertEquals(gcd.gcd(6, 4), 2);
        assertEquals(gcd.gcd(6, 9), 3);
        assertEquals(gcd.gcd(10, 20), 10);
        assertEquals(gcd.gcd(10, 21), 1);
    }

    /** Generates all possible combinations of pairs from the list.*/
    public <T> List<Pair<T, T>> genPairs(List<T> list) {
        List<Pair<T, T>> combinations = new ArrayList<>();

        for (int i = 0; i < list.size(); i++) {
            for (int j = 0; j < list.size(); j++) {
                combinations.add(new Pair<>(list.get(i), list.get(j)));
            }
        }
        return combinations;
    }

    @Test
    public void resultIsDivisor() {

        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 20, 30, 22, 33, 25, 55, 60);

        genPairs(numbers).forEach(pair -> {
            int a = pair.getKey();
            int b = pair.getValue();

            int result = gcd.gcd(a, b);
            System.out.println(String.format("testing in resultIsDivisor: gcd(%d %d) = %d", a, b, result));
            assertEquals(a % result, 0);
            assertEquals(b % result, 0);
        });

    }

    @Test
    public void resultIsPositive() {
        List<Integer> numbers = Arrays.asList(-1, 1, 2, -3, 4, -5, 6, 7, 8, 9, 15);

        genPairs(numbers).forEach(pair -> {
            int a = pair.getKey();
            int b = pair.getValue();

            int result = gcd.gcd(a, b);
            System.out.println(String.format("testing in resultIsPositive: gcd(%d %d) = %d", a, b, result));
            assertTrue(result > 0);

        });
    }

    @Test
    public void divisorIsGreatest() {
        List<Integer> numbers = Arrays.asList(1, 2, -3, 4, -5, 6, 7, 8, 9, 20, 30, 22, 33, 25, 55, 60);

        genPairs(numbers).forEach(pair -> {
            int a = pair.getKey();
            int b = pair.getValue();

            int result = gcd.gcd(a, b);
            System.out.println(String.format("testing in divisorIsGreatest: gcd(%d %d) = %d", a, b, result));

            assertTrue(result > 0);

            assertEquals(a % result, 0);
            assertEquals(b % result, 0);


            for (int i = result + 1; i < Math.min(a, b); i++) {
                assertFalse(String.format("gcd(%d, %d) = %d. There is a number %d, where %d %% %d == 0 and %d %% %d == 0",
                        a, b, result, i, a, i, b, i),
                        (a % i == 0) && (b % i == 0));
            }

        });

    }


    @Test(timeout = 200)
    public void testBorders() {
        assertEquals(gcd.gcd(Integer.MAX_VALUE, Integer.MAX_VALUE), Integer.MAX_VALUE);
        assertEquals(gcd.gcd(Integer.MIN_VALUE, Integer.MIN_VALUE), Integer.MIN_VALUE);
        assertEquals(gcd.gcd(Integer.MIN_VALUE, 4), 4);
    }
}