diff --git a/src/Control/Director.php b/src/Control/Director.php
index 05ca57f2f..ba61cfbd3 100644
--- a/src/Control/Director.php
+++ b/src/Control/Director.php
@@ -188,7 +188,6 @@ class Director implements TemplateGlobalProvider
         $cookies = array(),
         &$request = null
     ) {
-
         Config::nest();
         Injector::nest();
 
diff --git a/src/Core/AppKernel.php b/src/Core/AppKernel.php
index 792ceafd6..0002a7b7f 100644
--- a/src/Core/AppKernel.php
+++ b/src/Core/AppKernel.php
@@ -13,6 +13,7 @@ use SilverStripe\Core\Cache\ManifestCacheFactory;
 use SilverStripe\Core\Config\ConfigLoader;
 use SilverStripe\Core\Config\CoreConfigFactory;
 use SilverStripe\Core\Injector\Injector;
+use SilverStripe\Core\Injector\InjectorLoader;
 use SilverStripe\Core\Injector\SilverStripeServiceConfigurationLocator;
 use SilverStripe\Core\Manifest\ClassLoader;
 use SilverStripe\Core\Manifest\ClassManifest;
@@ -38,9 +39,10 @@ class AppKernel extends CoreKernel
 
         // Initialise the dependency injector as soon as possible, as it is
         // subsequently used by some of the following code
+        $injectorLoader = InjectorLoader::inst();
         $injector = new Injector(array('locator' => SilverStripeServiceConfigurationLocator::class));
-        $this->setContainer($injector);
-        Injector::set_inst($injector);
+        $injectorLoader->pushManifest($injector);
+        $this->setInjectorLoader($injectorLoader);
 
         // Manifest cache factory
         $manifestCacheFactory = $this->buildManifestCacheFactory();
diff --git a/src/Core/Config/Config.php b/src/Core/Config/Config.php
index 28a530446..15f1c127d 100644
--- a/src/Core/Config/Config.php
+++ b/src/Core/Config/Config.php
@@ -87,7 +87,7 @@ abstract class Config
     {
         // Unnest unless we would be left at 0 manifests
         $loader = ConfigLoader::inst();
-        if ($loader->countManifests() < 2) {
+        if ($loader->countManifests() <= 1) {
             user_error(
                 "Unable to unnest root Config, please make sure you don't have mis-matched nest/unnest",
                 E_USER_WARNING
diff --git a/src/Core/Config/ConfigLoader.php b/src/Core/Config/ConfigLoader.php
index ec39262d2..b5ca19d12 100644
--- a/src/Core/Config/ConfigLoader.php
+++ b/src/Core/Config/ConfigLoader.php
@@ -82,14 +82,31 @@ class ConfigLoader
     }
 
     /**
-     * Nest the current manifest
+     * Nest the config loader and activates it
      *
-     * @return ConfigCollectionInterface
+     * @return static
      */
     public function nest()
     {
-        $manifest = $this->getManifest()->nest();
-        $this->pushManifest($manifest);
-        return $manifest;
+        // Nest config
+        $manifest = clone $this->getManifest();
+
+        // Create new blank loader with new stack (top level nesting)
+        $newLoader = new self;
+        $newLoader->pushManifest($manifest);
+
+        // Activate new loader
+        return $newLoader->activate();
+    }
+
+    /**
+     * Mark this instance as the current instance
+     *
+     * @return $this
+     */
+    public function activate()
+    {
+        static::$instance = $this;
+        return $this;
     }
 }
diff --git a/src/Core/CoreKernel.php b/src/Core/CoreKernel.php
index 4509c863a..7e81e436c 100644
--- a/src/Core/CoreKernel.php
+++ b/src/Core/CoreKernel.php
@@ -5,6 +5,7 @@ namespace SilverStripe\Core;
 use InvalidArgumentException;
 use SilverStripe\Core\Config\ConfigLoader;
 use SilverStripe\Core\Injector\Injector;
+use SilverStripe\Core\Injector\InjectorLoader;
 use SilverStripe\Core\Manifest\ClassLoader;
 use SilverStripe\Core\Manifest\ModuleLoader;
 use SilverStripe\View\ThemeResourceLoader;
@@ -14,6 +15,11 @@ use SilverStripe\View\ThemeResourceLoader;
  */
 class CoreKernel implements Kernel
 {
+    /**
+     * @var Kernel
+     */
+    protected $nestedFrom = null;
+
     /**
      * @var Injector
      */
@@ -39,6 +45,11 @@ class CoreKernel implements Kernel
      */
     protected $configLoader = null;
 
+    /**
+     * @var InjectorLoader
+     */
+    protected $injectorLoader = null;
+
     /**
      * @var ThemeResourceLoader
      */
@@ -54,21 +65,44 @@ class CoreKernel implements Kernel
 
     public function nest()
     {
-        // TODO: Implement nest() method.
+        // Clone this kernel, nesting config / injector manifest containers
+        $kernel = clone $this;
+        $kernel->setConfigLoader($this->configLoader->nest());
+        $kernel->setInjectorLoader($this->injectorLoader->nest());
+        return $kernel;
+    }
+
+    public function activate()
+    {
+        $this->configLoader->activate();
+        $this->injectorLoader->activate();
+        return $this;
+    }
+
+    public function getNestedFrom()
+    {
+        return $this->nestedFrom;
     }
 
     public function getContainer()
     {
-        return $this->container;
+        return $this->getInjectorLoader()->getManifest();
     }
 
-    public function setContainer(Injector $container)
+    public function setInjectorLoader(InjectorLoader $injectorLoader)
     {
-        $this->container = $container;
-        $container->registerService($this, Kernel::class);
+        $this->injectorLoader = $injectorLoader;
+        $injectorLoader
+            ->getManifest()
+            ->registerService($this, Kernel::class);
         return $this;
     }
 
+    public function getInjectorLoader()
+    {
+        return $this->injectorLoader;
+    }
+
     public function getClassLoader()
     {
         return $this->classLoader;
diff --git a/src/Core/HTTPApplication.php b/src/Core/HTTPApplication.php
index abd24d5ad..ff1bcbac7 100644
--- a/src/Core/HTTPApplication.php
+++ b/src/Core/HTTPApplication.php
@@ -106,10 +106,14 @@ class HTTPApplication implements Application
      */
     public function execute(callable $callback)
     {
-        return $this->callMiddleware(function () use ($callback) {
-            // Pre-request boot
-            $this->getKernel()->boot();
-            return call_user_func($callback);
-        });
+        try {
+            return $this->callMiddleware(function () use ($callback) {
+                // Pre-request boot
+                $this->getKernel()->boot();
+                return call_user_func($callback);
+            });
+        } finally {
+            $this->getKernel()->shutdown();
+        }
     }
 }
diff --git a/src/Core/Injector/Injector.php b/src/Core/Injector/Injector.php
index 52b76c7c7..6b3f28abd 100644
--- a/src/Core/Injector/Injector.php
+++ b/src/Core/Injector/Injector.php
@@ -236,18 +236,7 @@ class Injector implements ContainerInterface
      */
     public static function inst()
     {
-        return self::$instance;
-    }
-
-    /**
-     * Sets the default global injector instance.
-     *
-     * @param Injector $instance
-     * @return Injector Reference to new active Injector instance
-     */
-    public static function set_inst(Injector $instance)
-    {
-        return self::$instance = $instance;
+        return InjectorLoader::inst()->getManifest();
     }
 
     /**
@@ -262,11 +251,10 @@ class Injector implements ContainerInterface
      */
     public static function nest()
     {
-        $current = self::$instance;
-
-        $new = clone $current;
-        $new->nestedFrom = $current;
-        return self::set_inst($new);
+        // Clone current injector and nest
+        $new = clone self::inst();
+        InjectorLoader::inst()->pushManifest($new);
+        return $new;
     }
 
     /**
@@ -277,15 +265,17 @@ class Injector implements ContainerInterface
      */
     public static function unnest()
     {
-        if (self::inst()->nestedFrom) {
-            self::set_inst(self::inst()->nestedFrom);
-        } else {
+        // Unnest unless we would be left at 0 manifests
+        $loader = InjectorLoader::inst();
+        if ($loader->countManifests() <= 1) {
             user_error(
                 "Unable to unnest root Injector, please make sure you don't have mis-matched nest/unnest",
                 E_USER_WARNING
             );
+        } else {
+            $loader->popManifest();
         }
-        return self::inst();
+        return static::inst();
     }
 
     /**
diff --git a/src/Core/Injector/InjectorLoader.php b/src/Core/Injector/InjectorLoader.php
new file mode 100644
index 000000000..fbba4b37b
--- /dev/null
+++ b/src/Core/Injector/InjectorLoader.php
@@ -0,0 +1,109 @@
+<?php
+
+namespace SilverStripe\Core\Injector;
+
+use BadMethodCallException;
+
+/**
+ * Registers chained injectors
+ */
+class InjectorLoader
+{
+    /**
+     * @internal
+     * @var self
+     */
+    private static $instance;
+
+    /**
+     * @var Injector[] map of injector instances
+     */
+    protected $manifests = array();
+
+    /**
+     * @return self
+     */
+    public static function inst()
+    {
+        return self::$instance ? self::$instance : self::$instance = new self();
+    }
+
+    /**
+     * Returns the currently active class manifest instance that is used for
+     * loading classes.
+     *
+     * @return Injector
+     */
+    public function getManifest()
+    {
+        if (empty($this->manifests)) {
+            throw new BadMethodCallException("No injector manifests available");
+        }
+        return $this->manifests[count($this->manifests) - 1];
+    }
+
+    /**
+     * Returns true if this class loader has a manifest.
+     *
+     * @return bool
+     */
+    public function hasManifest()
+    {
+        return (bool)$this->manifests;
+    }
+
+    /**
+     * Pushes a class manifest instance onto the top of the stack.
+     *
+     * @param Injector $manifest
+     */
+    public function pushManifest(Injector $manifest)
+    {
+        $this->manifests[] = $manifest;
+    }
+
+    /**
+     * @return Injector
+     */
+    public function popManifest()
+    {
+        return array_pop($this->manifests);
+    }
+
+    /**
+     * Check number of manifests
+     *
+     * @return int
+     */
+    public function countManifests()
+    {
+        return count($this->manifests);
+    }
+
+    /**
+     * Nest the config loader
+     *
+     * @return static
+     */
+    public function nest()
+    {
+        // Nest config
+        $manifest = $this->getManifest()->nest();
+
+        // Create new blank loader with new stack (top level nesting)
+        $newLoader = new self;
+        $newLoader->pushManifest($manifest);
+
+        // Activate new loader
+        $newLoader->activate();
+        return $newLoader;
+    }
+
+    /**
+     * Mark this instance as the current instance
+     */
+    public function activate()
+    {
+        static::$instance = $this;
+    }
+}
diff --git a/src/Core/Kernel.php b/src/Core/Kernel.php
index 7b7d979f8..6541fc8d9 100644
--- a/src/Core/Kernel.php
+++ b/src/Core/Kernel.php
@@ -4,6 +4,7 @@ namespace SilverStripe\Core;
 
 use SilverStripe\Core\Config\ConfigLoader;
 use SilverStripe\Core\Injector\Injector;
+use SilverStripe\Core\Injector\InjectorLoader;
 use SilverStripe\Core\Manifest\ClassLoader;
 use SilverStripe\Core\Manifest\ModuleLoader;
 use SilverStripe\View\ThemeResourceLoader;
@@ -42,23 +43,22 @@ interface Kernel
     /**
      * Nests this kernel, all components, and returns the nested value.
      *
-     * @return static
+     * @return Kernel
      */
     public function nest();
 
+    /**
+     * Ensures this kernel is the active kernel after or during nesting
+     *
+     * @return $this
+     */
+    public function activate();
+
     /**
      * @return Injector
      */
     public function getContainer();
 
-    /**
-     * Sets injector
-     *
-     * @param Injector $container
-     * @return $this
-     */
-    public function setContainer(Injector $container);
-
     /**
      * @return ClassLoader
      */
@@ -70,6 +70,19 @@ interface Kernel
      */
     public function setClassLoader(ClassLoader $classLoader);
 
+    /**
+     * Get loader for injector instance
+     *
+     * @return InjectorLoader
+     */
+    public function getInjectorLoader();
+
+    /**
+     * @param InjectorLoader $injectorLoader
+     * @return $this
+     */
+    public function setInjectorLoader(InjectorLoader $injectorLoader);
+
     /**
      * @return ModuleLoader
      */
diff --git a/src/Core/TestKernel.php b/src/Core/TestKernel.php
index b19551463..3fa8091ed 100644
--- a/src/Core/TestKernel.php
+++ b/src/Core/TestKernel.php
@@ -35,4 +35,10 @@ class TestKernel extends AppKernel
     {
         return true;
     }
+
+    protected function bootErrorHandling()
+    {
+        // Leave phpunit to capture errors
+        restore_error_handler();
+    }
 }
diff --git a/src/Dev/ExtensionTestState.php b/src/Dev/ExtensionTestState.php
index acd7c5c1e..5df311a04 100644
--- a/src/Dev/ExtensionTestState.php
+++ b/src/Dev/ExtensionTestState.php
@@ -37,7 +37,9 @@ class ExtensionTestState implements TestState
 
     public function setUpOnce($class)
     {
-        $isAltered = false;
+        // May be altered by another class
+        $isAltered = $this->extensionsToReapply || $this->extensionsToRemove;
+
         /** @var string|SapphireTest $class */
         /** @var string|DataObject $dataClass */
         // Remove any illegal extensions that are present
@@ -84,18 +86,19 @@ class ExtensionTestState implements TestState
             }
         }
 
-        // If we have made changes to the extensions present, then migrate the database schema.
-        if ($isAltered || $this->extensionsToReapply || $this->extensionsToRemove || $class::getExtraDataObjects()) {
+        // clear singletons, they're caching old extension info
+        // which is used in DatabaseAdmin->doBuild()
+        Injector::inst()->unregisterObjects(DataObject::class);
+
+        // If we have altered the schema, but SapphireTest::setUpBeforeClass() would not otherwise
+        // reset the schema (if there were extra objects) then force a reset
+        if ($isAltered && empty($class::getExtraDataObjects())) {
             DataObject::reset();
             if (!SapphireTest::using_temp_db()) {
                 SapphireTest::create_temp_db();
             }
-            SapphireTest::resetDBSchema(true);
+            $class::resetDBSchema(true);
         }
-
-        // clear singletons, they're caching old extension info
-        // which is used in DatabaseAdmin->doBuild()
-        Injector::inst()->unregisterObjects(DataObject::class);
     }
 
     public function tearDownOnce($class)
diff --git a/src/Dev/SapphireTest.php b/src/Dev/SapphireTest.php
index 910ad4cce..e72f6747a 100644
--- a/src/Dev/SapphireTest.php
+++ b/src/Dev/SapphireTest.php
@@ -203,11 +203,11 @@ class SapphireTest extends PHPUnit_Framework_TestCase
      */
     protected function setUp()
     {
+        // Reset state
         self::$kernel->reset();
 
-        //nest config and injector for each test so they are effectively sandboxed per test
-        Config::nest();
-        Injector::nest();
+        // Nest
+        self::$kernel->nest();
 
         // Call state helpers
         static::$state->setUp($this);
@@ -299,12 +299,20 @@ class SapphireTest extends PHPUnit_Framework_TestCase
         // Reset kernel
         static::$kernel->reset();
 
-        //nest config and injector for each suite so they are effectively sandboxed
-        Config::nest();
-        Injector::nest();
+        // Nest kernel
+        static::$kernel->nest();
 
         // Call state helpers
         static::$state->setUpOnce(static::class);
+
+        // Build DB if we have objects
+        if (static::getExtraDataObjects()) {
+            DataObject::reset();
+            if (!self::using_temp_db()) {
+                self::create_temp_db();
+            }
+            static::resetDBSchema(true);
+        }
     }
 
     /**
@@ -322,14 +330,14 @@ class SapphireTest extends PHPUnit_Framework_TestCase
         // Call state helpers
         static::$state->tearDownOnce(static::class);
 
-        //unnest injector / config now that the test suite is over
-        // this will reset all the extensions on the object too (see setUpBeforeClass)
-        Injector::unnest();
-        Config::unnest();
-
-        static::resetDBSchema();
+        // Unnest
+        static::$kernel->activate();
 
+        // Reset PHP state
         static::$kernel->reset();
+
+        // Reset DB schema
+        static::resetDBSchema();
     }
 
     /**
@@ -485,11 +493,10 @@ class SapphireTest extends PHPUnit_Framework_TestCase
         }
 
         // Call state helpers
-        static::$state->setUp($this);
+        static::$state->tearDown($this);
 
-        //unnest injector / config now that tests are over
-        Injector::unnest();
-        Config::unnest();
+        // Unnest
+        self::$kernel->activate();
 
         // Reset state
         self::$kernel->reset();
@@ -992,6 +999,11 @@ class SapphireTest extends PHPUnit_Framework_TestCase
         }
     }
 
+    /**
+     * Create temp DB without creating extra objects
+     *
+     * @return string
+     */
     public static function create_temp_db()
     {
         // Disable PHPUnit error handling
diff --git a/src/Dev/TestSession.php b/src/Dev/TestSession.php
index 22d7042cc..794c3b45d 100644
--- a/src/Dev/TestSession.php
+++ b/src/Dev/TestSession.php
@@ -53,10 +53,10 @@ class TestSession
 
     public function __construct()
     {
-        $this->session = Injector::inst()->create('SilverStripe\\Control\\Session', array());
-        $this->cookies = Injector::inst()->create('SilverStripe\\Control\\Cookie_Backend');
+        $this->session = Injector::inst()->create(Session::class, array());
+        $this->cookies = Injector::inst()->create(Cookie_Backend::class);
         $this->controller = new Controller();
-        $this->controller->setSession($this->session);
+        // @todo - Ensure $this->session is set on all requests
         $this->controller->pushCurrent();
     }