ProjectFactory.php

<?php

use App\Client;
use App\Project;
use Faker\Generator as Faker;

$factory->define(Project::class, function (Faker $faker) {
    return [
        'title' => $faker->sentence,
    ];
});

$factory->afterMakingState(Project::class, 'reuse', function (Project $project, $faker) {
    $project->client_id = Client::query()->inRandomOrder()->first()->getKey();
});