[TASK] Use a per-test subject in KeyFrameTest

Similar to #963.

Author: oliverklee

tests/Unit/CSSList/KeyFrameTest.php

@@ -15,37 +15,33 @@
  */
 final class KeyFrameTest extends TestCase
 {
-    /**
-     * @var KeyFrame
-     */
-    private $subject;
-
-    protected function setUp(): void
-    {
-        $this->subject = new KeyFrame();
-    }
-
     /**
      * @test
      */
     public function implementsAtRule(): void
     {
-        self::assertInstanceOf(AtRule::class, $this->subject);
+        $subject = new KeyFrame();
+
+        self::assertInstanceOf(AtRule::class, $subject);
     }
 
     /**
      * @test
      */
     public function implementsRenderable(): void
     {
-        self::assertInstanceOf(Renderable::class, $this->subject);
+        $subject = new KeyFrame();
+
+        self::assertInstanceOf(Renderable::class, $subject);
     }
 
     /**
      * @test
      */
     public function implementsCommentable(): void
     {
-        self::assertInstanceOf(Commentable::class, $this->subject);
+        $subject = new KeyFrame();
+
+        self::assertInstanceOf(Commentable::class, $subject);
     }
 }