public function testCheckCourseCommented()
 {
     $course = Course::all()->random();
     $user = factory(User::class, 1)->create();
     $this->assertEquals(false, $this->repository->checkCourseCommented($user->stu_id, $course->id));
     factory(Comment::class, 1)->create(['course_id' => $course->id, 'commenter' => $user->stu_id]);
     $this->assertEquals(true, $this->repository->checkCourseCommented($user->stu_id, $course->id));
 }