input: Write a python function to test a POST request to the '/users' endpoint using Flask's test client.
  assert create_user({'username': 'john', 'email': 'john@example.com'}) == {'status': 'user created'}
  assert create_user({'username': 'jane', 'email': 'jane@example.com'}) == {'status': 'user created'}
  assert create_user({'username': 'doe', 'email': 'doe@example.com'}) == {'status': 'user created'}
output: def create_user(data):
      from flask import Flask, jsonify, request
  
      app = Flask(__name__)
  
      @app.route('/users', methods=['POST'])
      def users():
          if request.method == 'POST':
              req_data = request.get_json()
              username = req_data.get('username')
              email = req_data.get('email')
              if username and email:
                  return jsonify({'status': 'user created'}), 201
              return jsonify({'status': 'missing parameters'}), 400
      
      with app.test_client() as client:
          response = client.post('/users', json=data)
          return response.get_json()