diff --git a/src/Core/Extensible.php b/src/Core/Extensible.php
index e23823d1c..de40620b6 100644
--- a/src/Core/Extensible.php
+++ b/src/Core/Extensible.php
@@ -3,12 +3,9 @@
 namespace SilverStripe\Core;
 
 use InvalidArgumentException;
-use SilverStripe\Control\RequestHandler;
 use SilverStripe\Core\Config\Config;
 use SilverStripe\Core\Injector\Injector;
 use SilverStripe\Dev\Deprecation;
-use SilverStripe\ORM\DataExtension;
-use SilverStripe\ORM\DataObject;
 use SilverStripe\View\ViewableData;
 
 /**
@@ -214,6 +211,14 @@ trait Extensible
         return true;
     }
 
+    /**
+     * Clears all cached extra_methods cache data
+     */
+    public static function flush_extra_methods_cache()
+    {
+        self::$extra_methods = [];
+    }
+
 
     /**
      * Remove an extension from a class.
diff --git a/src/Dev/State/ExtensionTestState.php b/src/Dev/State/ExtensionTestState.php
index 29c4dd09c..4aeec1f48 100644
--- a/src/Dev/State/ExtensionTestState.php
+++ b/src/Dev/State/ExtensionTestState.php
@@ -30,6 +30,7 @@ class ExtensionTestState implements TestState
      */
     public function setUp(SapphireTest $test)
     {
+        DataObject::flush_extra_methods_cache();
     }
 
     public function tearDown(SapphireTest $test)
@@ -104,23 +105,5 @@ class ExtensionTestState implements TestState
 
     public function tearDownOnce($class)
     {
-        // @todo: This isn't strictly necessary to restore extensions, but only to ensure that
-        // Object::$extra_methods is properly flushed. This should be replaced with a simple
-        // flush mechanism for each $class.
-        /** @var string|DataObject $dataClass */
-
-        // Remove extensions added for testing
-        foreach ($this->extensionsToRemove as $dataClass => $extensions) {
-            foreach ($extensions as $extension) {
-                $dataClass::remove_extension($extension);
-            }
-        }
-
-        // Reapply ones removed
-        foreach ($this->extensionsToReapply as $dataClass => $extensions) {
-            foreach ($extensions as $extension) {
-                $dataClass::add_extension($extension);
-            }
-        }
     }
 }
diff --git a/tests/php/Core/Injector/InjectorTest.php b/tests/php/Core/Injector/InjectorTest.php
index 47c428ceb..b1dee54db 100644
--- a/tests/php/Core/Injector/InjectorTest.php
+++ b/tests/php/Core/Injector/InjectorTest.php
@@ -1065,6 +1065,7 @@ class InjectorTest extends SapphireTest
         /** @var Member|SomeExtension $member */
         $member = new Member();
         $this->assertTrue($member->hasExtension(SomeExtension::class));
+        $this->assertTrue($member->hasMethod('someMethod'));
         $this->assertSame('bar', $member->someMethod());
     }
 }
diff --git a/tests/php/Core/Injector/InjectorTest/SomeCustomisedExtension.php b/tests/php/Core/Injector/InjectorTest/SomeCustomisedExtension.php
index 8599558e4..9641d7df1 100644
--- a/tests/php/Core/Injector/InjectorTest/SomeCustomisedExtension.php
+++ b/tests/php/Core/Injector/InjectorTest/SomeCustomisedExtension.php
@@ -2,7 +2,9 @@
 
 namespace SilverStripe\Core\Tests\Injector\InjectorTest;
 
-class SomeCustomisedExtension extends SomeExtension
+use SilverStripe\Dev\TestOnly;
+
+class SomeCustomisedExtension extends SomeExtension implements TestOnly
 {
     public function someMethod()
     {
diff --git a/tests/php/Core/Injector/InjectorTest/SomeExtension.php b/tests/php/Core/Injector/InjectorTest/SomeExtension.php
index 3f7e60ef4..4de0ab9c8 100644
--- a/tests/php/Core/Injector/InjectorTest/SomeExtension.php
+++ b/tests/php/Core/Injector/InjectorTest/SomeExtension.php
@@ -2,9 +2,10 @@
 
 namespace SilverStripe\Core\Tests\Injector\InjectorTest;
 
+use SilverStripe\Dev\TestOnly;
 use SilverStripe\ORM\DataExtension;
 
-class SomeExtension extends DataExtension
+class SomeExtension extends DataExtension implements TestOnly
 {
     public function someMethod()
     {