PHPunit：测试问题

I have run into a major problem while writing tests. I am using Laravel 5.6.0 as framework and PHPUnit 7.0 for testing. As a testing DB I have used sqlite with storage in memory. This is from my database.php:

'sqlite_testing' => [
    'driver'   => 'sqlite',
    'database' => ':memory:',
    'prefix'   => '',
],

But my problem is that I have several places where I use whereRaw, for example $query->whereRaw('STR_TO_DATE(CONCAT(date, " ",from), "%Y-%m-%d %k") < ?', [$before]);. The problem here is that sqlite does not have the STR_TO_DATE or CONCAT functions that MySQL has. So PHPUnut throws a bunch of errors because of that.

My solution was instead using a MySQL DB as testing DB. But this doesn't seem to work since I get several different errors, mostly I have several tests where foreign key constraint fails.

One exaple for this is that I have the following in my Base TestCase setUp method:

if (Schema::hasTable('gym_schedule') && !empty(GymSchedule::createGymSchedules())) {
    $this->artisan('db:seed', ['--class' => 'GymScheduleTableSeeder']);
}

This fails every time except the first because it says that a schedùle with id 1 already exists (id is my primary key). I did try to truncate all tables between each test class using tearDown, but that did not help at all, and also the testing became reeeeally slow, like 3 seconds for each test.

So basically that approach does not work either.

I am at a loss. I have tried googling this and searching through StackOverflow. I am open to any suggestion that is not too complicated (either remove all MySQL functions somehow, solve usage of MySQL or anything else really).

Does anyone have a good idea?