input: Write a python function to connect to a MongoDB Atlas Cluster, insert a document, retrieve documents, and close the connection.
  assert len(retrieve_documents()) > 0
  assert isinstance(retrieve_documents()[0], dict)
  assert 'name' in retrieve_documents()[0]
output: def manage_mongodb():
      from pymongo import MongoClient
  
      def connect_to_mongodb():
          uri = "your_mongodb_atlas_connection_string"
          client = MongoClient(uri)
          return client
  
      def insert_document(client, db_name, collection_name, document):
          db = client[db_name]
          collection = db[collection_name]
          collection.insert_one(document)
  
      def retrieve_documents(client, db_name, collection_name):
          db = client[db_name]
          collection = db[collection_name]
          return list(collection.find())
  
      def close_connection(client):
          client.close()
  
      client = connect_to_mongodb()
      db_name = "your_db_name"
      collection_name = "your_collection_name"
      document = {"name": "John Doe", "age": 30, "email": "john.doe@example.com"}
  
      insert_document(client, db_name, collection_name, document)
      documents = retrieve_documents(client, db_name, collection_name)
      close_connection(client)
  
      return documents
  
  def retrieve_documents():
      return manage_mongodb()