input: Write a python function to fetch and print country details from the World Bank API.
  assert fetch_country_details() is None
output: def fetch_country_details():
      import requests
  
      url = 'http://api.worldbank.org/v2/country/all?format=json'
      response = requests.get(url)
      
      if response.status_code == 200:
          data = response.json()
          countries = data[1]
          for country in countries:
              print(f"Name: {country['name']}, Capital: {country['capitalCity']}, Region: {country['region']['value']}")
      else:
          print(f"Failed to fetch data: {response.status_code}")