Added test for the GCD algorithm

[anhpham197]

I saw that there was no testing for GCD algorithm, so I decided to write some test for the function gcd (int num1, int num2) based on MC/DC standard.

dir: src/test/java/com.thealgorithms/maths/GCDTest

`package com.thealgorithms.maths;

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

public class GCDTest {

@Test
void test1() {
    Assertions.assertThrows(ArithmeticException.class, () -> GCD.gcd(-1,0));
}

@Test
void test2() {
    Assertions.assertThrows(ArithmeticException.class, () -> GCD.gcd(10, -2));
}

@Test
void test3() {
    Assertions.assertThrows(ArithmeticException.class, () -> GCD.gcd(-5, -3));
}

@Test
void test4() {
    Assertions.assertEquals(GCD.gcd(0, 2), 2);
}

@Test
void test5() {
    Assertions.assertEquals(GCD.gcd(10, 0), 10);
}

@Test
void test6() {
    Assertions.assertEquals(GCD.gcd(1, 0), 1);
}

@Test
void test7() {
    Assertions.assertEquals(GCD.gcd(9, 6), 3);
}

}`

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[github-actions]

Please reopen this issue once you add more information and updates here. If this is not the case and you need some help, feel free to seek help from our Gitter or ping one of the reviewers. Thank you for your contributions!