input: Write a function to create a basic REST API using Python and Flask to list all the countries in the world. The function should initialize a Flask app, define a route to fetch the countries from a JSON file, and return the list of countries as a JSON response. Ensure the function includes the necessary Flask and JSON imports and sets up the Flask app correctly.
  
  
  assert create_country_api() is not None
  # Testing the API route to ensure it returns a JSON response
  assert 'Italy' in create_country_api().get('/countries').json()
  assert 'Japan' in create_country_api().get('/countries').json()
  assert 'Germany' in create_country_api().get('/countries').json()
  
output: def create_country_api():
      from flask import Flask, jsonify
      import json
  
      app = Flask(__name__)
  
      @app.route('/countries', methods=['GET'])
      def get_countries():
          with open('countries.json', 'r') as file:
              countries = json.load(file)
          return jsonify(countries)
  
      return app