allow tests to utilise the null logger (#38785)

src/Illuminate/Log/LogManager.php

@@ -95,7 +95,7 @@ public function channel($channel = null)
      */
     public function driver($driver = null)
     {
-        return $this->get($driver ?? $this->getDefaultDriver());
+        return $this->get($this->parseDriver($driver));
     }
 
     /**
@@ -450,7 +450,7 @@ protected function configurationFor($name)
     /**
      * Get the default log driver name.
      *
-     * @return string
+     * @return string|null
      */
     public function getDefaultDriver()
     {
@@ -490,13 +490,30 @@ public function extend($driver, Closure $callback)
      */
     public function forgetChannel($driver = null)
     {
-        $driver = $driver ?? $this->getDefaultDriver();
+        $driver = $this->parseDriver($driver);
 
         if (isset($this->channels[$driver])) {
             unset($this->channels[$driver]);
         }
     }
 
+    /**
+     * Parse the driver name.
+     *
+     * @param  string|null  $driver
+     * @return string|null
+     */
+    protected function parseDriver($driver)
+    {
+        $driver = $driver ?? $this->getDefaultDriver();
+
+        if ($this->app->runningUnitTests()) {
+            $driver = $driver ?? 'null';
+        }
+
+        return $driver;
+    }
+
     /**
      * System is unusable.
      *

tests/Log/LogManagerTest.php

@@ -15,6 +15,7 @@
 use Monolog\Logger as Monolog;
 use Orchestra\Testbench\TestCase;
 use ReflectionProperty;
+use RuntimeException;
 
 class LogManagerTest extends TestCase
 {
@@ -203,6 +204,41 @@ public function testLogManagerCreatesMonologHandlerWithProperFormatter()
         }
     }
 
+    public function testItUtilisesTheNullDriverDuringTestsWhenNullDriverUsed()
+    {
+        $config = $this->app->make('config');
+        $config->set('logging.default', null);
+        $config->set('logging.channels.null', [
+            'driver' => 'monolog',
+            'handler' => NullHandler::class,
+        ]);
+        $manager = new class($this->app) extends LogManager
+        {
+            protected function createEmergencyLogger()
+            {
+                throw new RuntimeException('Emergency logger was created.');
+            }
+        };
+
+        // In tests, this should not need to create the emergency logger...
+        $manager->info('message');
+
+        // we should also be able to forget the null channel...
+        $this->assertCount(1, $manager->getChannels());
+        $manager->forgetChannel();
+        $this->assertCount(0, $manager->getChannels());
+
+        // However in production we want it to fallback to the emergency logger...
+        $this->app['env'] = 'production';
+        try {
+            $manager->info('message');
+
+            $this->fail('Emergency logger was not created as expected.');
+        } catch (RuntimeException $exception) {
+            $this->assertSame('Emergency logger was created.', $exception->getMessage());
+        }
+    }
+
     public function testLogManagerCreateSingleDriverWithConfiguredFormatter()
     {
         $config = $this->app['config'];