[6.x] Replace Event Dispatcher in resolved cache repositories when Event::fake() is used

[colindecarlo]

The fake and fakeFor method of the Event facade currently fails to replace the existing Event Dispatcher with the faked dispatcher in resolved cache repositories.

I've found that making assertions on cache events is a pretty useful way of testing code that uses the cache under the hood. For instance:

class Calculator {

    public function add($operand1, $operand2)
    {
        $cacheKey = sprintf("%s+%s", $operand1, $operand2);

        if (Cache::has($cacheKey)) {
            return Cache::get($cacheKey);
        }

        $result = $operand1 + $operand2;

        Cache::put($cacheKey, $result);

        return $result;
    }
}

class CalculatorTest {

    public function test_it_returns_calculations_from_cache()
    {
        Cache::put('1+1', 3);
        Event::fake();

        $calculator = new Calculator;

        $this->assertEquals(3, $calculator->add(1, 1));

        Event::assertDispatched(CacheHit::class, function ($hit) {
            return $hit->key == '1+1' && $hit->value == 3;
        });
    }
}

This PR adds a public method to the CacheManager used to refresh each cache repositories to which it holds a reference to with the event dispatcher that is currently bound in the service container.

The method is called in the Event::fake and Event::fakeFor methods.

A getEventDispatcher method was added to the cache Repository class to make testing a little easier.

[taylorotwell]

So does it not work already if you call Event::fake() first instead of after Cache::put?

[colindecarlo]

In some cases yes, all that is required is to put the call to Event::fake before accessing the cache. However, after some debugging, it looks like if you include the RefreshDatabase trait then bootstrapping the app includes the ArtisanServiceProvider which makes all the commands, some of which require the cache (for instance RestartQueueCommand). In these cases the cache is created during the test setup so it gets the real event dispatcher.