gistfile1.py

from mock import Mock, patch
import requests

class VSSecureMailWS:
    def encrypt_and_send(self, url, data):
        r = requests.post(url)
        if r.status_code == 200:
            return "{0} {1}".format(data, r.text)
        else:
            return "Error"

mock_response = Mock()
mock_response.status_code = 200
mock_response.text = "world"

with patch('requests.post') as mock_post:
    mock_post.return_value = mock_response
    
    v = VSSecureMailWS()
    assert v.encrypt_and_send("http://foo.com/", "hello") == "hello world"