Using laravel's HTTP tests, test the CustomerController's store method, make sure to mock the mailable "WelcomeNewCustomer" using mail-fake.

StoreCustomer.php

<?php

namespace Tests\Feature;

use Tests\TestCase;
use App\Mail\WelcomeNewCustomer;
use Illuminate\Support\Facades\Mail;

class StoreCustomer extends TestCase
{
    /**
     * A basic feature test example.
     *
     * @return void
     */
    public function test_store_customer()
    {
        Mail::fake();
        $data = [
            'name' => $this->faker->name,
            'email' => $this->faker->email,
        ];
        $response = $this->post(route('customer.store'), $data);
        Mail::assertNothingSent();
        Mail::assertSent(WelcomeNewCustomer::class);
        $response->assertStatus(201)->assertJson($data);
    }
}