tests: ensure output mocking is disabled so we can actually catch the output (#1018)

Discovered via https://github.com/barryvdh/laravel-ide-helper/pull/1017#issuecomment-679318764

This only happens if you run an artisan command _before_ `runCommand`,
but since every of these tests performs migrations, using artisan,
the mocked output instance is left behind and also affected us.

The call added in `runCommand` explicitly unregisters
`\Illuminate\Console\OutputStyle` and thus also throwing away possibly
mocked versions.

tests/TestCase.php

@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace Barryvdh\LaravelIdeHelper\Tests;
 
 use Illuminate\Console\Command;
+use Illuminate\Console\OutputStyle;
 use Orchestra\Testbench\TestCase as BaseTestCase;
 use Spatie\Snapshots\MatchesSnapshots;
 use Symfony\Component\Console\Tester\CommandTester;
@@ -29,6 +30,9 @@ abstract class TestCase extends BaseTestCase
      */
     protected function runCommand(Command $command, array $arguments = [], array $interactiveInput = []): CommandTester
     {
+        // TODO: once Laravel 5.5 is dropped, call `$this->withoutMockingConsoleOutput()` instead
+        $this->app->offsetUnset(OutputStyle::class);
+
         $command->setLaravel($this->app);
 
         $tester = new CommandTester($command);