What should I put on `working_directory`?

I have this config

version: 2
    working_directory: /var/www/html
      - image: circleci/php:7.3.3
      - image: circleci/mysql:5.7
          MYSQL_USER: homestead
          MYSQL_ROOT_PASSWORD: secret
          MYSQL_DATABASE: blog_test
      # Installation
      - run:
          name: Install System Packages
          command: sudo apt-get update && sudo apt-get -y install git unzip zlib1g-dev
      - run:
          name: Install PHP Extensions
          command: |
            sudo docker-php-ext-install pdo
            sudo docker-php-ext-install pdo_mysql
            sudo docker-php-ext-install zip
            sudo apt install -y mysql-client
      - run:
          name: Install Composer
          command: |
            php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');" && \
            php -r "if (hash_file('SHA384', 'composer-setup.php') === trim(file_get_contents('https://composer.github.io/installer.sig'))) { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;" && \
            php composer-setup.php && \
            php -r "unlink('composer-setup.php');" && \
            chmod +x ./composer.phar && \
            mv ./composer.phar /usr/local/bin/composer

  # Dependencies
  - checkout
  - run: composer install --prefer-dist --no-interaction
  - run: ./bin/phpunit --version

  # Database
  - run: ./bin/console doctrine:database:create --env=test --no-interaction
  - run: ./bin/console doctrine:schema:create --env=test --no-interaction
  - run: ./bin/console doctrine:fixtures:load --env=test --no-interaction

  # To use server:start we need to install pcntl extension
  - run:
      name: Run web server in background
      command: ./bin/console server:run
      background: true

  # Testing
  - run: ./bin/phpunit

But it return error on Checkout code
Directory (/var/www/html) you are trying to checkout to is not empty and not a git repository
What should I set working_directory to?

Ok, now I understand that you can put anything into working_directory. When checking out code, it will be put there.

But I still don’t understand why that directory is not empty, and not a git repository?

Ok, now I understand why directory not empty. It is because I install composer in it. Should’ve install it in another directory.