Laravel单元/模型测试

I've been following the Testing Laravel series on Laracasts and am now trying to set up a project according to the TDD and wishfull thinking principles.

Well, I'm at my second test, and I'm confused whether or not it should be a test at all. I have a Customer model that I'd like to test for creation. But I'm unsure how to do this, since factory(Customer::class)->create(); already creates a Customer.

What would insert/update tests for a Model look like? Are they not neccesary or am I setting up my tests in the wrong way?

At the moment this is my test:

/** @test */
public function it_can_add_a_customer()
{
    factory(Customer::class)->create();

    $customers = Customer::all();

    $this->assertCount(1, $customers);
}