Tennis Match Laracasts Kata - https://laracasts.com/series/code-katas-with-phpunit/episodes/6

Player.php

<?php

namespace App;

class Player
{
    /**
     * @var string
     */
    public string $name;

    /**
     * @var int
     */
    public int $points = 0;

    /**
     * Create a new player.
     *
     * @param  string  $name
     */
    public function __construct(string $name)
    {
        $this->name = $name;
    }

    /**
     * Add a point for the player.
     */
    public function score()
    {
        $this->points++;
    }

    /**
     * Convert the player's score to the Tennis term.
     *
     * @return string
     */
    public function toTerm(): string
    {
        switch ($this->points) {
            case 0:
                return 'love';
            case 1:
                return 'fifteen';
            case 2:
                return 'thirty';
            case 3:
                return 'forty';
        }
    }
}

TennisMatch.php

<?php

namespace App;

class TennisMatch
{
    /**
     * @var Player
     */
    protected Player $playerOne;

    /**
     * @var Player
     */
    protected Player $playerTwo;

    /**
     * Create a new TennisMatch.
     *
     * @param  Player  $playerOne
     * @param  Player  $playerTwo
     */
    public function __construct(Player $playerOne, Player $playerTwo)
    {
        $this->playerOne = $playerOne;
        $this->playerTwo = $playerTwo;
    }

    /**
     * Score the match.
     *
     * @return string
     */
    public function score(): string
    {
        if ($this->hasWinner()) {
            return 'Winner: '.$this->leader()->name;
        }

        if ($this->hasAdvantage()) {
            return 'Advantage: '.$this->leader()->name;
        }

        if ($this->isDeuce()) {
            return 'deuce';
        }

        return sprintf(
            "%s-%s",
            $this->playerOne->toTerm(),
            $this->playerTwo->toTerm(),
        );
    }

    /**
     * Get the current leader of the set.
     *
     * @return Player
     */
    protected function leader(): Player
    {
        return $this->playerOne->points > $this->playerTwo->points
            ? $this->playerOne
            : $this->playerTwo;
    }

    /**
     * Determine if the players are in deuce.
     *
     * @return bool
     */
    protected function isDeuce(): bool
    {
        if (! $this->hasReachedDeuceThreshold()) {
            return false;
        }

        return $this->playerOne->points === $this->playerTwo->points;
    }

    /**
     * Determine if both players have scored at least 3 points.
     *
     * @return bool
     */
    protected function hasReachedDeuceThreshold(): bool
    {
        return $this->playerOne->points >= 3 && $this->playerTwo->points >= 3;
    }

    /**
     * Determine if one player has the advantage.
     *
     * @return bool
     */
    protected function hasAdvantage(): bool
    {
        if (! $this->hasReachedDeuceThreshold()) {
            return false;
        }

        return ! $this->isDeuce();
    }

    /**
     * Determine if there is a winner.
     *
     * @return bool
     */
    protected function hasWinner(): bool
    {
        if ($this->playerOne->points < 4 && $this->playerTwo->points < 4) {
            return false;
        }

        return abs($this->playerOne->points - $this->playerTwo->points) >= 2;
    }
}

TennisMatchTest.php

<?php

use App\Player;
use App\TennisMatch;
use PHPUnit\Framework\TestCase;

class TennisMatchTest extends TestCase
{
    /**
     * @test
     * @dataProvider scores
     */
    function it_scores_a_tennis_match($playerOnePoints, $playerTwoPoints, $score)
    {
        $match = new TennisMatch(
            $john = new Player('John'),
            $jane = new Player('Jane'),
        );

        for ($i = 0; $i < $playerOnePoints; $i++) {
            $john->score();
        }

        for ($i = 0; $i < $playerTwoPoints; $i++) {
            $jane->score();
        }

        $this->assertEquals($score, $match->score());
    }

    public function scores()
    {
        return [
            [0, 0, 'love-love'],
            [1, 0, 'fifteen-love'],
            [1, 1, 'fifteen-fifteen'],
            [2, 0, 'thirty-love'],
            [3, 0, 'forty-love'],
            [2, 2, 'thirty-thirty'],
            [3, 3, 'deuce'],
            [4, 4, 'deuce'],
            [5, 5, 'deuce'],
            [4, 3, 'Advantage: John'],
            [3, 4, 'Advantage: Jane'],
            [4, 0, 'Winner: John'],
            [0, 4, 'Winner: Jane'],
        ];
    }
}