[9.x] Improve test for prepend and push in Repository Class (#43833)

we have to check item are exist and didn't destory in array

Author: moharami

tests/Config/RepositoryTest.php

@@ -173,13 +173,21 @@ public function testSetArray()
 
     public function testPrepend()
     {
+        $this->assertSame('aaa', $this->repository->get('array.0'));
+        $this->assertSame('zzz', $this->repository->get('array.1'));
         $this->repository->prepend('array', 'xxx');
         $this->assertSame('xxx', $this->repository->get('array.0'));
+        $this->assertSame('aaa', $this->repository->get('array.1'));
+        $this->assertSame('zzz', $this->repository->get('array.2'));
     }
 
     public function testPush()
     {
+        $this->assertSame('aaa', $this->repository->get('array.0'));
+        $this->assertSame('zzz', $this->repository->get('array.1'));
         $this->repository->push('array', 'xxx');
+        $this->assertSame('aaa', $this->repository->get('array.0'));
+        $this->assertSame('zzz', $this->repository->get('array.1'));
         $this->assertSame('xxx', $this->repository->get('array.2'));
     }