When testing filament plugins you most certainly won't have a User Model so you will have to create one in order to login to filament and navigate and execute functions within your new plugin.

I will try to explain the process I followed to do this:

#Create a User model for testing.

# file: tests/Models/User.php
 
class User extends Model implements FilamentUser
{
    protected $guarded = [];
    public $timestamps = false;
    protected $table = 'users';
    public function canAccessFilament(): bool
    {
        return true;
    }
}

#A TestCase file with the database creation and the proper Filament providers. You may include any extra migration or setup code that your plugin requires.

# file: tests/TestCase.php
 
class TestCase extends Orchestra
{
    protected User $adminUser;
 
    protected function setUp(): void
    {
        parent::setUp();
 
        $this->setUpDatabase($this->app);
 
    }
 
    protected function getPackageProviders($app)
    {
        return [
            // Filament Service providers...
            BladeHeroiconsServiceProvider::class,
            BladeIconsServiceProvider::class,
            FilamentServiceProvider::class,
            FormsServiceProvider::class,
            LivewireServiceProvider::class,
            SupportServiceProvider::class,
            TablesServiceProvider::class,
 
            // Your package service provider...
            EmailMessageServiceProvider::class,
            FilamentEmailLogServiceProvider::class,
        ];
    }
 
    protected function setUpDatabase($app)
    {
        $app['db']->connection()->getSchemaBuilder()->create('users', function (Blueprint $table) {
            $table->increments('id');
            $table->string('email');
            $table->string('name');
        });
 
        $this->adminUser = User::create(['email' => '[email protected]', 'name' => 'Admin']);
    }
}

#Now in your tests you can use $this->adminUser for logging to filament.

# file: tests/MyTest.php
 
it('redirects on non logged users', function () {
    $this->get(Config::get('filament.path'))
        ->assertRedirect();
});
 
 
it('shows dashboard to logged users', function () {
    actingAs($this->adminUser)
      ->get(Config::get('filament.path'))
      ->assertSuccessful();
});
 
 
it('can render EmailResourcePage', function () {
    actingAs($this->adminUser)
      ->get(EmailResource::getUrl('index'))
      ->assertSuccessful();
});

Hope I made myself clear. If you would like to view a complete example please take a look at my filament-email-log plugin.