How do we turn event handling back on for test after ->withoutEvents?

I have a class that emits an event which ultimately sends an email. For most of the tests for that class, I don't want an email sent, so this is my setUp function:

public function setUp()
{
    parent::setUp();

    $this->withoutEvents();
}

In one specific test, I would like to enable event handling again, to make sure the e-mail is submitted. I've tried this:

/** @test */
public function it_sends_a_welcome_email_when_new_user_registers()
{
    $this->app->instance('events', new Dispatcher);
    Mail::fake();

    $mock = factory(User::class)->make()->toArray();
    $mock['password'] = 'something';
    $mock['password_confirmation'] = 'something';

    $this->json('post', '/register', $mock)
        ->assertStatus(200);

    Mail::assertSent(WelcomeEmail::class);
}

It didn't work. Laravel doesn't include a ->withEvents function, either. If I disable the call to ->withoutEvents(), the tests run slower, and I receive several e-mail messages. The Mail fake doesn't work, though, unless I disable the call to app->instance, also.

I can split the test into another file, one with events and one without, but that seems clumsy. Is there a better way?