Friday, 31 January 2014

Testing webapps from Python with Selenium

I'm a great believer in tests to ensure code quality, although naturally I don't always practise what I preach. Recently I've been working on a webapp with a Python server backend. I can test the server independently of the webapp, but testing the webapp itself involves clicking on various things, waiting for the server to respond, and then checking the result. Doing this manually quickly becomes a chore and that's without even considering different browsers.

The solution is Python of course (as usual on this blog). The aptly-named Selenium allows you to automate this sort of thing from the point of view of writing tests. It's available in several languages (I think they all use the same server backend) but I'm going to focus here on the Python. "pip install selenium" on Windows installs the basics; this will allow you to test against Firefox and Safari. For Chrome and IE, you need to download two additional files and add them to the PATH.

The Selenium docs are a bit confusing because (a) they keep referring back to an earlier version of the software (Selenium 1) which had different behaviour and (b) the commands for the Selenium IDE are very similar but not the same as the commands for the Python bindings.

Anyhoo, here's a modified version of the Selenium script that I'm using just to give some idea of how it works. When you run this at the command-line, a new Firefox window pops up, resizes to the specified dimensions, flies through the test, shuts down, and then I get the usual unittest output from the Python script. Specifying a browser name (e.g. Chrome) runs the test against Chrome instead.

import sys
import unittest

from selenium import webdriver
from selenium.webdriver.common.action_chains import ActionChains

import as ui

browsers = {"firefox": webdriver.Firefox, "ie": webdriver.Ie, "chrome": webdriver.Chrome, "safari": webdriver.Safari}

class Tests(unittest.TestCase):
    def setUp(self):
        self.driver = browser()
        self.driver.set_window_size(1380, 880)

        # Convenience functions
        self.driver.by_id = self.driver.find_element_by_id
        self.driver.by_xpath = self.driver.find_element_by_xpath
        self.wait = ui.WebDriverWait(self.driver, 5)

    def test_the_webpage(self):
        d = self.driver

        self.drag_and_drop(d.by_id("ID1"), d.by_xpath("//div[@id='things']/img[3]"))
        self.wait.until(lambda d: d.by_xpath("//table[@id='results']"))
        self.assertEqual("45", d.by_xpath("//table[@id='results']/tbody/tr/td[2]").text)

        self.wait.until(lambda d: d.by_xpath("//table[@id='results']"))
        self.assertEqual("64", d.by_xpath("//table[@id='results']/tbody/tr/td[2]").text)

    def drag_and_drop(self, elem, target):
        ActionChains(self.driver).drag_and_drop(elem, target).perform()

    def tearDown(self):

if __name__ == "__main__":
    browsername = "firefox"
    if len(sys.argv) == 2:
        browsername = sys.argv[1].lower()
    browser = browsers[browsername]

    suite = unittest.TestLoader().loadTestsFromTestCase(Tests)
Note: For another Python project related to browser automation, see also twill.


Shane said...

What Python version are you running? I am getting an error line 13, in setUp
self.driver = browser()
NameError: global name 'browser' is not defined

Noel O'Boyle said...

I can't remember, but I'd assume Python 2.7. Probably a better way of organising the code is where browser is defined in the SetUp of each of four subclasses of a main test class. This wouldn't then rely on any globals.

Anonymous said...


Can you please confirm me one thing. I have worked on selenium using Java and TestNG framework. Now, I am switching to Python + Selenium.

Can I use testNG with this combination too. If yes, how or if no, which alternate is available ?

Bill Maca said...

self.driver = browser() should be self.driver = browsers()

Bill Maca said...

There is a bug in the code.

# this Global variable browser does not exist
def setUp(self):
self.driver = browser()

#change it to this
def setUp(self):
self.driver = browsers()

Bill Maca said...

There is a bug in the code

#global var browser i snot defined
def setUp(self):
self.driver = browser()

#should be changed to this
def setUp(self):
self.driver = browsers()