在 Laravel 中创建可测试的外观

Here's a cheat sheet on how to make your simple service class more useful by adding dependency injection, a facade, and a way to easily swap in a fake.

The skeleton is simple:

• The original service class
• Create a contract the service class abides by
• In a service provider, register the service class in the container
• Create a facade
• Create a fake implementation of the contract that can be swapped for testing

The original service class

Here's our original service class that we are starting with (apologies for not having a compelling example, but it isn't really necessary to contrive one for this).

<?php namespace App\Foo;

class FooService
{
    public function foo(): string
    {
        return 'bar';
    }

    public function fizz(): string
    {
        return 'buzz';
    }
}

The contract

First, we should create a contract so we can ensure that our eventual fake and our original service both meet expectations. As well as any future implementations.

<?php namespace App\Foo\Contracts;

interface Foo
{
    public function foo(): string;

    public function fizz(): string;
}

Don't forget to make sure the service implements it.

<?php namespace App;

use App\Foo\Contracts\Foo;

class FooService implements Foo
{
   // ...
}

Binding to the container

Next, we should bind the concrete implementation to the contract in our service provider.

<?php namespace App\Providers;

use App\Foo\Contracts\Foo;
use App\FooService;
use Illuminate\Support\ServiceProvider;

class AppServiceProvider extends ServiceProvider
{
    /**
     * Register any application services.
     */
    public function register(): void
    {
        $this->app->bind(Foo::class, FooService::class);
    }

   // ...
}

The facade

Now, we can create our facade class.

<?php namespace App\Foo\Facades;

use Illuminate\Support\Facades\Facade;

/**
* @method static string foo(): string
* @method static string fizz(): string
*/
class Foo extends Facade
{
    protected static function getFacadeAccessor(): string
    {
        return \App\Foo\Contracts\Foo::class;
    }
}

The facade simply needs the name of the binding it will pull from the container to be returned from getFacadeAccessor. In our case, that's the name of the contract that currently has our service bound to it.

Note that if you want IDE support, you'll have to re-define the method signatures in the doc block above the class.

At this point, we can use our facade.

Usage

<?php namespace App\Http\Controllers;

use App\Foo\Facades\Foo;

class FooController extends Controller
{
    public function index()
    {
        return response()->json([
            'foo' => Foo::foo(),
        ]);
    }
}

Alternatively, we can also inject it as a dependency.

<?php namespace App\Http\Controllers;

use App\Foo\Contracts;

class FooController extends Controller
{
   public function __construct(protected Foo $foo) {}

    public function index()
    {
        return response()->json([
            'foo' => $this->foo->foo(),
        ]);
    }
}

Faking the facade

Laravel often offers a neat way to easily fake its facades, e.g. Event::fake(). We can implement this ourselves.

All we have to do is create the fake implementation of our contract, then add the fake method to our facade.

<?php namespace App\Foo;

use App\Foo\Contracts\Foo;

class FakeFooService implements Foo
{
    public function __construct(public Foo $actual) {}

    public function foo(): string
    {
        return 'fake';
    }

    public function fizz(): string
    {
        return 'very fake';
    }
}

In our fake implementation, we also create a public reference to the "actual" concrete class.

And here is our facade fake implementation. You can see we utilize that reference to actual.

<?php namespace App\Foo\Facades;

use App\Foo\FakeFooService;
use Illuminate\Support\Facades\Facade;

/**
* @method static string foo(): string
* @method static string fizz(): string
*/
class Foo extends Facade
{
    public static function fake()
    {
        $actual = static::isFake()
            ? static::getFacadeRoot()->actual
            : static::getFacadeRoot();

        tap(new FakeFooService($actual), function ($fake) {
            static::swap($fake);
        });
    }

   // ...
}

A basic test

Now let's write a quick test that hits the controller example we created above.

<?php namespace Tests\Feature;

use App\Foo\Facades\Foo;
use Illuminate\Testing\Fluent\AssertableJson;
use Tests\TestCase;

class FooTest extends TestCase
{
    public function test_foo(): void
    {
        $response = $this->get('/');

        $response->assertJson(fn (AssertableJson $json)
            => $json->where('foo', 'bar'));
    }

    public function test_fake_foo(): void
    {
        Foo::fake();

        $response = $this->get('/');

        $response->assertJson(fn (AssertableJson $json)
            => $json->where('foo', 'fake'));
    }
}

The tests are not useful but they show how easy it is to use our fake. In test_fake_foo we get foo=fake while test_foo returns foo=bar.

Taking testing further

The fun thing about fakes is that in our fake implementation, we can add extra methods to test anything we may find useful. For example, we could slap a counter in our fake's foo method that increments every time we call foo. Then we could add a method called assertFooCount where we can assert that the method was called as many times as we are expecting.

<?php namespace App\Foo;

use App\Foo\Contracts\Foo;
use Illuminate\Testing\Assert;

class FakeFooService implements Foo
{
    public int $fooCount = 0;

    public function __construct(public Foo $actual) {}

    public function foo(): string
    {
        $this->fooCount++;

        return 'fake';
    }

    public function fizz(): string
    {
        return 'very fake';
    }

    public function assertFooCount(int $count)
    {
        Assert::assertSame($this->fooCount, $count);
    }
}

As you can see we use Laravel's Illuminate\Testing\Assert to make the assertion. Then our test can look like this.

public function test_incrementor(): void
{
    Foo::fake();

    Foo::foo();
    Foo::foo();
    Foo::foo();

    Foo::assertFooCount(3); // pass!
}

That's it!

Not everything needs a facade, but when you are building tools/packages that are used internally, a facade is often a strong pattern to rely upon.

Here's the repo with all the code: https://github.com/ClintWinter/laravel-facade-example

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