What Is the Page Object in Selenium?

Right from Selenium’s documentation:

"Page Object is a Design Pattern which has become popular in test automation for enhancing test maintenance and reducing code duplication. A page object is an object-oriented class that serves as an interface to a page of your AUT. The tests then use the methods of this page object class whenever they need to interact with the UI of that page. The benefit is that if the UI changes for the page, the tests themselves don’t need to change, only the code within the page object needs to change. Subsequently, all changes to support that new UI are located in one place."

The Page Object Design Pattern provides the following advantages:

1. There is a clean separation between test code and page specific code such as locators (or their use if you’re using a UI Map) and layout.

2. There is a single repository for the services or operations offered by the page rather than having these services scattered throughout the tests.

In both cases, this allows any modifications required due to UI changes to all be made in one place. Useful information on this technique can be found on numerous blogs as this ‘test design pattern’ is becoming widely used. We encourage the reader who wishes to know more to search the internet for blogs on this subject. Many have written on this design pattern and can provide useful tips beyond the scope of this user guide. To get you started, though, we’ll illustrate page objects with a simple example.

First, consider an example, typical of test automation, that does not use a page object.

/***
 * Tests login feature
 */
public class Login {

        public void testLogin() {
                selenium.type("inputBox", "testUser");
                selenium.type("password", "my supersecret password");
                selenium.click("sign-in");
                selenium.waitForPageToLoad("PageWaitPeriod");
                Assert.assertTrue(selenium.isElementPresent("compose button"),
                                "Login was unsuccessful");
        }
}

There are two problems with this approach:

1. There is no separation between the test method and the AUT’s locators (IDs in this example); both are intertwined in a single method. If the AUT’s UI changes its identifiers, layout, or how a login is input and processed, the test itself must change.

2. The ID-locators would be spread in multiple tests, in all tests that had to use this login page.

Applying the page object techniques, this example could be rewritten like this in the following example of a page object for a Sign-in page.

/**
 * Page Object encapsulates the Sign-in page.
 */
public class SignInPage {

        private Selenium selenium;

        public SignInPage(Selenium selenium) {
                this.selenium = selenium;
                if(!selenium.getTitle().equals("Sign in page")) {
                        throw new IllegalStateException("This is not sign in page, current page is: "
                                        +selenium.getLocation());
                }
        }

        /**
         * Login as valid user
         *
         * @param userName
         * @param password
         * @return HomePage object
         */
        public HomePage loginValidUser(String userName, String password) {
                selenium.type("usernamefield", userName);
                selenium.type("passwordfield", password);
                selenium.click("sign-in");
                selenium.waitForPageToLoad("waitPeriod");

                return new HomePage(selenium);
        }
}

And the page object for the homepage could look like this:

/**
 * Page Object encapsulates the Home Page
 */
public class HomePage {

        private Selenium selenium;

        public HomePage(Selenium selenium) {
                if (!selenium.getTitle().equals("Home Page of logged in user")) {
                        throw new IllegalStateException("This is not Home Page of logged in user, current page" +
                                        "is: " +selenium.getLocation());
                }
        }

        public HomePage manageProfile() {
                // Page encapsulation to manage profile functionality
                return new HomePage(selenium);
        }

        /*More methods offering the services represented by Home Page
        of Logged User. These methods in turn might return more Page Objects
        for example click on Compose mail button could return ComposeMail class object*/

}

So now, the login test would use these two page objects as follows:

/***
 * Tests login feature
 */
public class TestLogin {

        public void testLogin() {
                SignInPage signInPage = new SignInPage(selenium);
                HomePage homePage = signInPage.loginValidUser("userName", "password");
                Assert.assertTrue(selenium.isElementPresent("compose button"),
                                "Login was unsuccessful");
        }
}

There is a lot of flexibility in how the page objects may be designed, but there are a few basic rules for getting the desired maintainability of your test code.

Page objects themselves should never make verifications or assertions. This is part of your test and should always be within the test’s code, never in a page object. The page object will contain the representation of the page, and the services the page provides via methods but no code related to what is being tested should be within the page object.

There is one, single verification which can, and should, be within the page object and that is to verify that the page, and possibly critical elements on the page, were loaded correctly. This verification should be done while instantiating the page object. In the examples above, both the SignInPage and HomePage constructors check that the expected page is available and ready for requests from the test.

A page object does not necessarily need to represent an entire page. The Page Object design pattern could be used to represent components on a page. If a page in the AUT has multiple components, it may improve maintainability if there is a separate page object for each component.

There are other design patterns that also may be used in testing. Some use a Page Factory for instantiating their page objects. Discussing all of these is beyond the scope of this user guide. Here, we merely want to introduce the concepts to make the reader aware of some of the things that can be done. As was mentioned earlier, many have blogged on this topic and we encourage the reader to search for blogs on these topics.