InvalidArgumentException: json_decode error: Syntax error - laravel

Question

I'm upgrading from Laravel 6 to 7 and when I run phpunit I get this error in some tests
InvalidArgumentException: json_decode error: Syntax error
But if in the ReindexJob.php file I change the function
public function handle(): void
{
$this->channel->items()->searchable();
}
to
public function handle(): void
{
$this->channel->items();
}
I no longer have the error, but this line should not be changed.
My composer.json is here
"require": {
"php": "^7.2.5|^8.0",
"laravel/framework": "^7.29",
"dingo/api": "^3.0",
"laravel/socialite": "^4.2",
"socialiteproviders/slack": "^3.0",
"doctrine/dbal": "^2.5",
"pusher/pusher-php-server": "~3.0",
"nesbot/carbon": "^2.0",
"league/flysystem-aws-s3-v3": "^1.0",
"google/apiclient": "^2.10",
"laravel/tinker": "^2.5",
"jaspaul/eloquent-model-validation": "^2.0",
"soapbox/goodtalk-settings": "^2.0",
"symfony/var-dumper": "^5.0",
"fideloper/proxy": "^4.4",
"socialiteproviders/microsoft-graph": "^2.0",
"layershifter/tld-extract": "^1.2",
"spatie/laravel-query-builder": "^2.1",
"microsoft/microsoft-graph": "^1.1",
"soapbox/signed-requests": "^4.2",
"predis/predis": "^1.1",
"laravel/horizon": "^4.3",
"jaspaul/eloquent-sti": "^2.0",
"jshayes/fake-requests": "^4.1",
"laravel/cashier": "^10.0",
"soapbox/truncator": "^1.0",
"soapbox/idempotency": "^5.0",
"jshayes/laravel-datadogstatsd": "^2.0",
"algolia/scout-extended": "^1.18",
"segmentio/analytics-php": "^1.5",
"art4/json-api-client": "^0.10.0",
"soapbox/agenda-template-client": "^6.0",
"league/csv": "^9.7",
"vinkla/hashids": "^8.1",
"tymon/jwt-auth": "^1.0",
"socialiteproviders/microsoft-azure": "^3.0",
"joypixels/emoji-toolkit": "^6.0.1",
"h4cc/wkhtmltopdf-amd64": "0.12.x",
"barryvdh/laravel-snappy": "^0.4.7",
"league/mime-type-detection": "^1.4",
"laravel/slack-notification-channel": "^2.3",
"soapbox/laravel-rollout": "^3.0",
"fruitcake/laravel-cors": "^2.0",
"guzzlehttp/guzzle": "^6.3.1|^7.0.1",
"sentry/sentry-laravel": "^2.7"
},
"require-dev": {
"fzaninotto/faker": "~1.4",
"mockery/mockery": "1.0.*",
"phpunit/phpunit": "~8.0",
"symfony/css-selector": "^4.0",
"symfony/dom-crawler": "^4.0",
"squizlabs/php_codesniffer": "^2.6",
"friendsofphp/php-cs-fixer": "^2.1",
"brianium/paratest": "~3.0",
"filp/whoops": "~2.0",
"laravel/telescope": "^3.5",
"dms/phpunit-arraysubset-asserts": "^0.1.0"
},
"autoload": {
"classmap": [
"database"
],
"psr-4": {
"App\\": "app/"
}
},
"autoload-dev": {
"psr-4": {
"Tests\\": "tests/"
}
},
"scripts": {
"post-root-package-install": [
"php -r \"file_exists('.env') || copy('.env.example', '.env');\""
],
"post-create-project-cmd": [
"php artisan key:generate",
"php artisan jwt:generate"
],
"post-install-cmd": [
"Illuminate\\Foundation\\ComposerScripts::postInstall",
"./scripts/install-git-hooks"
],
"post-update-cmd": [
"Illuminate\\Foundation\\ComposerScripts::postUpdate"
],
"post-autoload-dump": [
"Illuminate\\Foundation\\ComposerScripts::postAutoloadDump",
"#php artisan package:discover"
]
},
"config": {
"bin-dir": "vendor/bin",
"preferred-install": "dist"
},
"minimum-stability": "dev",
"prefer-stable": true,
"extra": {
"laravel": {
"dont-discover": [
"dingo/api"
]
}
}
Apparently everything is correct here.
And some files with the same test are passing, but it can't be, because they are practically identical.