Impossible to specify per-bin cache backend service from within settings.php

Looks nice, some minor nitpicks...

1. +++ b/core/tests/Drupal/Tests/Core/Cache/CacheFactoryTest.php
   @@ -0,0 +1,120 @@
   + * Definition of Drupal\Tests\Core\Cache\CacheFactoryTest.
   

   Contains \Drupal\... ;)

2. +++ b/core/tests/Drupal/Tests/Core/Cache/CacheFactoryTest.php
   @@ -0,0 +1,120 @@
   +/**
   + * Tests the cache CacheFactory.
   + *
   + * @group Cache
   + */
   +class CacheFactoryTest extends UnitTestCase {
   

   Look at some of the new test classes, they use @coversDefaultClass + @covers on methods, we should do that her as well.

3. +++ b/core/tests/Drupal/Tests/Core/Cache/CacheFactoryTest.php
   @@ -0,0 +1,120 @@
   +    $container->expects($this->once())
   +      ->method('get')
   +      ->with('cache.backend.database')
   +      ->will($this->returnValue($builtin_default_backend_factory));
   

   I think most tests use an actual ContainerBuilder instead of mocking it, that's easier I think.

   It will also fail nicer (unknown service exception instead of fatal error)

4. +++ b/core/tests/Drupal/Tests/Core/Cache/CacheFactoryTest.php
   @@ -0,0 +1,120 @@
   +   * Test that the cache factory falls back to default contrib service.
   

   Wondering if we should use something else than contrib here, memory maybe? or example?

+++ b/core/tests/Drupal/Tests/Core/Cache/CacheFactoryTest.php
@@ -0,0 +1,123 @@
+/**
+ * @file
+ * Contains Drupal\Tests\Core\Cache\CacheFactoryTest.
+ */

Still missing a leading \, but can be fixed on commit...

Looks good, let's fix this.

Great work!

Committed/pushed to 8.x, thanks!

Arggh. 'fixed locally' yeah right...

Committed/pushed to 8.x, thanks!