input: Write a function to create a basic REST API using Python and Flask to list all the countries in the world. This function should instantiate a Flask application, define a route to fetch and return a list of countries from a JSON file, and start the Flask server if the module is executed directly. 
  assert create_country_api()=="""import flask
  from flask import Flask, request, jsonify
  import json
  
  app = Flask(\'__main__\')
  
  @app.route('/countries', methods=['GET'])
  def get_countries():
  \twith open('data.json', 'r') as f:
  \t countries = json.load(f)
  \t return jsonify(countries)
  
  if __name__ == 'main':
  \t app.run()""".strip()
  assert call_country_api()=="""import requests
  response = requests.get('http://127.0.0.1:5000/countries')
  response.json()""".strip()
  assert response_output()=="""[{"name": "Afghanistan", "capital": "Kabul"}, {"name": "Albania", "capital": "Tirana"}, {"name": "Algeria", "capital": "Algiers"}]""".strip()
output: 
  import flask
  from flask import Flask, request, jsonify
  import json
  
  app = Flask(__name__)
  
  @app.route('/countries', methods=['GET'])
  def get_countries():
      with open('data.json', 'r') as f:
          countries = json.load(f)
      return jsonify(countries)
  
  if __name__ == '__main__':
      app.run()
  