Matrix Addition puzzle

MatrixAddition.php

<?php
/**
 * Unit tests for Matrix Addition puzzle.
 *
 * Requirements: @see https://www.codewars.com/kata/matrix-addition
 * Write a function that accepts two square matrices (N x N two dimensional arrays),
 * and return the sum of the two.
 * Both matrices being passed into the function will be of size N x N (square),
 * containing only integers.
 *
 * How to sum two matrices:
 * Take each cell [n][m] from the first matrix,
 * and add it with the same [n][m] cell from the second matrix.
 * This will be cell [n][m] of the solution matrix.
 *
 * @package Cata\Tests\Unit\MatrixAddition
 * @author  Caspar Green <caspar@iCasparWebDevelopment.com>
 * @since   1.0.0
 */
declare(strict_types=1);

namespace Cata\Tests\Unit\MatrixAddition;

use Cata\MatrixAddition\MatrixAdder;
use PHPUnit\Framework\TestCase;

/**
 * Class MatrixAdderTest
 *
 * @package Cata\Tests\Unit\MatrixAddition
 * @since   1.0.0
 */
class MatrixAdderTest extends TestCase
{
    /**
     * A MatrixAdder instance.
     *
     * @var MatrixAdder
     */
    private $matrixAdder;

    /**
     * Set up before each test.
     *
     * @since 1.0.0
     *
     * @return void
     */
    protected function setUp()
    {
        $this->matrixAdder = new MatrixAdder();
    }

    /**
     * Test addMatrices() should return the matrix sum for (1x1) addends.
     *
     * @since 1.0.0
     *
     * @return void
     */
    public function testAddMatricesShouldReturnMatrixSumFor1x1(): void
    {
        $this->assertSame([[10]], $this->matrixAdder->addMatrices([[4]], [[6]]));
    }

    /**
     * Test addMatrices() should return the matrix sum for (2x2) matrix.
     *
     * Once we have this, we have a working algorithm for (N x N).
     *
     * @since 1.0.0
     *
     * @return void
     */

    public function testAddMatricesShouldReturnMatrixSumFor2x2(): void
    {
        $addend1 = [
            [3, 5],
            [4, 8],
        ];

        $addend2 = [
            [2, 7],
            [6, 3],
        ];

        $this->assertSame(
            [
                [5, 12],
                [10, 11],
            ],
            $this->matrixAdder->addMatrices($addend1, $addend2)
        );
    }
}

<?php
/**
 * Matrix Adder puzzle class
 *
 * @package Cata\MatrixAddition
 * @author  Caspar Green <caspar@iCasparWebDevelopment.com>
 * @since   1.0.0
 */
declare(strict_types=1);

namespace Cata\MatrixAddition;

/**
 * Class MatrixAdder
 *
 * @package Cata\MatrixAddition
 * @since   1.0.0
 */
class MatrixAdder
{
    /**
     * Add two matrices of integers.
     *
     * @param array $matrix1 First addend matrix.
     * @param array $matrix2 Second addend matrix.
     *
     * @since 1.0.0
     *
     * @return array
     */
    public function addMatrices(array $matrix1, array $matrix2): array
    {
        $sum = [];

        foreach ($matrix1 as $row => $cols) {
            foreach ($cols as $col => $value) {
                $sum[$row][$col] = $matrix1[$row][$col] + $matrix2[$row][$col];
            }
        }

        return $sum;
    }
}