Ouzo\Tests\Assert::that PHP Метод

    public static function that($subject)
    {
        return GeneralAssert::that($subject);
    }

 /**
  * @test
  */
 public function shouldFlattenNullValue()
 {
     //given
     $optional = Optional::of(Optional::of(Optional::fromNullable(null)));
     //when
     $result = $optional->flatten()->orNull();
     //then
     Assert::that($result)->isNull();
 }