While teaching Software Engineering I during the Winter 2013 term, I learned of a web testing suite named Selenium.
Enter Selenium. Now, here’s a way to not only automate web interactions, but to make them into automated unit tests for my research projects. This post is going to serve as a brief introduction to Selenium and how to start using it to interact with websites.
Selenium is a web automation framework that enables a user to essentially script a web site. In this post we’ll talk about using Selenium version 2, which is the main, up-to-date version of the software.
There are two main ways for you to interact with a website.
The Selenium IDE: Recording actions by Demonstration
First, you can use the Selenium IDE, which is a Firefox plugin that allows you to demonstrate interactions with a web site. You essentially record actions and then as you click around the page, type in form elements, and push buttons, the IDE records the actions for you in a pseudo-markup language. (If you happen to follow my other research, it is actually somewhat similar to CoScripter, another program-by-demonstration tool for the web, but with better web interaction and fewer features. For example, Selenium cannot store temporary data into tables.)
Thus, even with minimal web development or programming experience, you could create a script for Selenium that plays back, for example, a series of clicks on a page, completes a survey, or similar.
There are some limitations with the IDE. The main one that led me to using the WebDriver (below) is that it doesn’t interact very well with “contentEditable” div tags and other HTML5 elements.
Note that the Selenium IDE is version 1.x, which does NOT correspond to Selenium itself (which is version 2.x).
The Selenium WebDriver: Programming actions in code
The second way to interact with a website is using the Selenium Webdriver, which is a driver that essentially launches a website and then enables you to look through that website’s DOM to interact with elements on the page. Thus, you can use your own browser, like Firefox or Internet Explorer to load and navigate a web site.
Unfortunately, since Gidget isn’t available publicly yet, I can’t actually put tests on the blog that’ll directly run Gidget so instead I’ll use Google.
Building a Selenium Script
To install Selenium, you generally need to only type
pip install selenium
assuming that Python exists already on your system.
The first place I’m going to point you at is the Selenium Documentation Example of WebDriver, where they already include an example of making a query on Google. Here’s a reproduction of the code.
from selenium import webdriver from selenium.common.exceptions import TimeoutException from selenium.webdriver.support.ui import WebDriverWait from selenium.webdriver.support import expected_conditions as EC # Create a new instance of the Firefox driver driver = webdriver.Firefox() # go to the google home page driver.get("http://www.google.com") # find the element that's name attribute is q (the google search box) inputElement = driver.find_element_by_name("q") # type in the search inputElement.send_keys("Cheese!") # submit the form (although google automatically searches now without submitting) inputElement.submit() # the page is ajaxy so the title is originally this: print driver.title try: # we have to wait for the page to refresh, the last thing that seems to be updated is the title WebDriverWait(driver, 10).until(EC.title_contains("cheese!")) # You should see "cheese! - Google Search" print driver.title finally: driver.quit()
It works exactly as advertised and opens up a web browser, goes to Google, and then searches for “cheese!”. However, there are a number of features that are essential to actually testing web pages.
Waiting for Pages
The unfortunate reality of web pages nowadays is that you have to wait a lot. Whether it’s a form submit where you have to wait for the POST request to complete, or some really slow JQuery fading box, not everything you want to interact with is available. To get around this, you have to use the “wait” commands in Selenium.
The Selenium documents do provide a few examples but I had to do a lot of searching and testing to get things working so I’ll just provide my use cases here directly.
To wait for an element to appear in Selenium, you need to provide an explicit wait along with a condition. It basically waits until either the identified element loads, or until the timeout passes (at which point it will throw an exception). There is an example of that in the Selenium example above, but if you have Google Instant turned on, you’ll realise notice that Google now returns search results to you as soon as you start typing. How can you interact with page elements if you don’t even know what’s going to pop up, when?
In this case, we’re going to wait until the “Search Results” text pops up.
from selenium import webdriver from selenium.common.exceptions import TimeoutException from selenium.webdriver.support.ui import WebDriverWait from selenium.webdriver.support.ui import Select from selenium.webdriver.common.by import By from selenium.webdriver.support import expected_conditions as EC from selenium.common.exceptions import NoSuchElementException if __name__ == "__main__": driver = webdriver.Firefox() wait = WebDriverWait(driver, 100) driver.get("http://google.com") inputElement = driver.find_element_by_name("q") inputElement.send_keys("Irwin Kwan") wait.until(EC.element_to_be_clickable((By.XPATH, "//a[@href='http://irwinhkwan.wordpress.com/']"))) blog = driver.find_element_by_xpath("//a[@href='http://irwinhkwan.wordpress.com/']") blog.click() driver.quit()
Basically, the driver loads, we set up a “wait” that waits up to 100ms, and then we do a search on Google for my name. Note that we don’t actually submit the form – instead, we wait for the link to my blog to appear in the Google search results, find the element, then click on it. And yes, this is a cheap way to rack up those hits for my blog, so everyone run this code. 😉
There are a lot of expected conditions available in Selenium and this is probably the most important thing to be aware of when first starting. You can’t interact with page elements unless they’re available, after all. Here are some of the useful ones:
- EC.element_to_be_clickable: Wait for the element to be clickable. Good for elements that aren’t always visible or enabled. I use this a lot in the game.
- EC.visibility_of_element_located: Wait for the element to be visible. A lot of pages load all of their content, but hide it from the user. Here’s how you ensure that what’s being interacted with is actually visible.
- EC.presence_of_element_located: The element exists somewhere on the page.
There are a lot of these expected conditions. A full list is available on the selenium.webdriver.support.expected_conditions API document page.
The second key aspect here is the interaction. To do this, you have to “find” the element. So far, I’ve used two main ways of finding an element: ID, and XPath.
Finding elements by ID
Finding an element by ID is pretty much what it sounds like: searching for an element using its ID tag. ID tags are unique in the DOM and are therefore ideal for searching and testing. You can use it like this:
Finding elements by XPath
XPath is a query language designed to navigate XML. I won’t go through all of the details of XPath here, but I’ll present a few basic use cases. You basically can search on a number of conditions that you specify in the language so you can see if that element exists in the DOM.
- If you want to search if a specific tag exists:
- If you want to search for nested tags:
- If you want to search that text within the tags matches:
- If you want to search for text in attributes
With these two find_element commands, you can find most of what you need in your web pages. Selenium supports a number of other ways to search, including searching by CSS, but I haven’t needed to use it yet.
Dynamic Interactions with a Page
Another issue I encountered with the Gidget game is clicking through introduction text when I didn’t know how many pages were present. Essentially, the problem is that there’s a button that I have to push on the page, and if I push it a certain number of times, it’ll be disabled. However, I don’t know how many times I have to push it because it might be different each time.
I managed to get around this with a little fragment of code below:
wait.until(EC.element_to_be_clickable((By.ID, 'main_buttonMissionTextNext'))) while EC.element_to_be_clickable((By.ID,'main_buttonMissionTextNext')): driver.find_element_by_id("main_buttonMissionTextNext").click() if not driver.find_element_by_id("main_buttonMissionTextNext").click().is_enabled(): break wait.until(EC.element_to_be_clickable((By.ID, 'main_buttonMissionTextNext')))
There were two gotchas here: First, I wasn’t aware of it at the time, but the button was actually regenerated whenever you clicked it, so I had to search for it again when I clicked it. Second, I didn’t realise that there was an is_enabled() function you could use to test if an element is enabled or not. But now, you know!
Using the Selenium IDE and the Selenium WebDriver Together To Save Time
While writing code is nice and fun, HTML pages are very large and are covered with tags with various IDs. It becomes tedious very quickly, even with good web development debugging tools, to search through the DOM elements to identify what you need to interact with, then writing the code to search and click on it.
So work smarter, not harder and use the Selenium IDE. If you record your actions with a page and save it in the Selenium IDE, you can use “Export Test Case As… > Python 2 / unittest / WebDriver”. Now you have Python code for that series of actions that you just performed and can integrate it into your other tests.
In my case, I used the Selenium IDE to automatically complete an exit survey in Gidget, then exported it and used the code in my other test suites. It’s a great way to save time writing code.
Making your code into a Test Suite
In Python, the unit testing is built in. You simply have to import unittest, create a class that extends it, and then write your setup and teardown functions, along with a method beginning with “test”. Here’s the previous code for interacting with Google converted into a Python test suite.
import unittest from selenium import webdriver from selenium.common.exceptions import TimeoutException from selenium.webdriver.support.ui import WebDriverWait from selenium.webdriver.support.ui import Select from selenium.webdriver.common.by import By from selenium.webdriver.support import expected_conditions as EC from selenium.common.exceptions import NoSuchElementException class WebTester(unittest.TestCase): def setUp(self): self.driver = webdriver.Firefox() self.wait = WebDriverWait(self.driver, 100) def test_load_blog(self): self.driver.get("http://google.com") inputElement = self.driver.find_element_by_name("q") inputElement.send_keys("Irwin Kwan") self.wait.until(EC.element_to_be_clickable((By.XPATH, "//a[@href='http://irwinhkwan.wordpress.com/']"))) blog = self.driver.find_element_by_xpath("//a[@href='http://irwinhkwan.wordpress.com/']") blog.click() self.wait.until(EC.visibility_of_element_located((By.XPATH, "//h2[text()='Irwin Kwan']"))) self.assertTrue(self.driver.find_element_by_xpath("//h2[text()='Irwin Kwan']")) def tearDown(self): self.driver.quit() if __name__ == "__main__": unittest.main()
If you place multiple test suite classes in the file, unittest will run them all. Selenium will launch a new, fresh browser instance for each one as well.
Conclusion: Web Automation is Pretty Cool
I’m really just a new user. Selenium has a number of features that I haven’t needed and therefore don’t know much about. There’s a “remote control” mode that allows you to use a separate server to run tests for you. There are ways to store session variables, load specific Firefox profiles with add-ons, and there is a “Selenium server” mode as well. If you need these features, chances are you’ll be able to find information about them on the Selenium site documents.
I feel that this information should set most people up with enough information to get started with Selenium and making it work for them in a useful way. I hope that this post is useful to you guys!