ページオブジェクトモデル
Note: this page has merged contents from multiple sources, including the Selenium wiki
Overview
Within your web app’s UI, there are areas where your tests interact with. A Page Object only models these as objects within the test code. This reduces the amount of duplicated code and means that if the UI changes, the fix needs only to be applied in one place.
Page Object is a Design Pattern that 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.
Advantages
- There is a clean separation between the test code and page-specific code, such as locators (or their use if you’re using a UI Map) and layout.
- There is a single repository for the services or operations the page offers 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. Helpful information on this technique can be found on numerous blogs as this ‘test design pattern’ is becoming widely used. We encourage readers who wish to know more to search the internet for blogs on this subject. Many have written on this design pattern and can provide helpful tips beyond the scope of this user guide. To get you started, we’ll illustrate page objects with a simple example.
Examples
First, consider an example, typical of test automation, that does not use a page object:
/***
* Tests login feature
*/
public class Login {
public void testLogin() {
// fill login data on sign-in page
driver.findElement(By.name("user_name")).sendKeys("userName");
driver.findElement(By.name("password")).sendKeys("my supersecret password");
driver.findElement(By.name("sign-in")).click();
// verify h1 tag is "Hello userName" after login
driver.findElement(By.tagName("h1")).isDisplayed();
assertThat(driver.findElement(By.tagName("h1")).getText(), is("Hello userName"));
}
}
There are two problems with this approach.
- 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.
- 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.
import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
/**
* Page Object encapsulates the Sign-in page.
*/
public class SignInPage {
protected WebDriver driver;
// <input name="user_name" type="text" value="">
private By usernameBy = By.name("user_name");
// <input name="password" type="password" value="">
private By passwordBy = By.name("password");
// <input name="sign_in" type="submit" value="SignIn">
private By signinBy = By.name("sign_in");
public SignInPage(WebDriver driver){
this.driver = driver;
if (!driver.getTitle().equals("Sign In Page")) {
throw new IllegalStateException("This is not Sign In Page," +
" current page is: " + driver.getCurrentUrl());
}
}
/**
* Login as valid user
*
* @param userName
* @param password
* @return HomePage object
*/
public HomePage loginValidUser(String userName, String password) {
driver.findElement(usernameBy).sendKeys(userName);
driver.findElement(passwordBy).sendKeys(password);
driver.findElement(signinBy).click();
return new HomePage(driver);
}
}
and page object for a Home page could look like this.
import org.openqa.selenium.By;
import org.openqa.selenium.WebDriver;
/**
* Page Object encapsulates the Home Page
*/
public class HomePage {
protected WebDriver driver;
// <h1>Hello userName</h1>
private By messageBy = By.tagName("h1");
public HomePage(WebDriver driver){
this.driver = driver;
if (!driver.getTitle().equals("Home Page of logged in user")) {
throw new IllegalStateException("This is not Home Page of logged in user," +
" current page is: " + driver.getCurrentUrl());
}
}
/**
* Get message (h1 tag)
*
* @return String message text
*/
public String getMessageText() {
return driver.findElement(messageBy).getText();
}
public HomePage manageProfile() {
// Page encapsulation to manage profile functionality
return new HomePage(driver);
}
/* 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 {
@Test
public void testLogin() {
SignInPage signInPage = new SignInPage(driver);
HomePage homePage = signInPage.loginValidUser("userName", "password");
assertThat(homePage.getMessageText(), is("Hello userName"));
}
}
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.
Assertions in Page Objects
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 an 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.
Page Component Objects
A page object does not necessarily need to represent all the parts of a page itself. The same principles used for page objects can be used to create “Page Component Objects” that represent discrete chunks of the page and can be included in page objects. These component objects can provide references to the elements inside those discrete chunks, and methods to leverage the functionality provided by them.
For example, a Product page has multiple products.
<!-- Products Page -->
<div class="header_container">
<span class="title">Products</span>
</div>
<div class="inventory_list">
<div class="inventory_item">
</div>
<div class="inventory_item">
</div>
<div class="inventory_item">
</div>
<div class="inventory_item">
</div>
<div class="inventory_item">
</div>
<div class="inventory_item">
</div>
</div>
Each product is a component of the Products page.
<!-- Inventory Item -->
<div class="inventory_item">
<div class="inventory_item_name">Backpack</div>
<div class="pricebar">
<div class="inventory_item_price">$29.99</div>
<button id="add-to-cart-backpack">Add to cart</button>
</div>
</div>
The Product page HAS-A list of products. This relationship is called Composition. In simpler terms, something is composed of another thing.
public abstract class BasePage {
protected WebDriver driver;
public BasePage(WebDriver driver) {
this.driver = driver;
}
}
// Page Object
public class ProductsPage extends BasePage {
public ProductsPage(WebDriver driver) {
super(driver);
// No assertions, throws an exception if the element is not loaded
new WebDriverWait(driver, Duration.ofSeconds(3))
.until(d -> d.findElement(By.className("header_container")));
}
// Returning a list of products is a service of the page
public List<Product> getProducts() {
return driver.findElements(By.className("inventory_item"))
.stream()
.map(e -> new Product(e)) // Map WebElement to a product component
.toList();
}
// Return a specific product using a boolean-valued function (predicate)
// This is the behavioral Strategy Pattern from GoF
public Product getProduct(Predicate<Product> condition) {
return getProducts()
.stream()
.filter(condition) // Filter by product name or price
.findFirst()
.orElseThrow();
}
}
The Product component object is used inside the Products page object.
public abstract class BaseComponent {
protected WebElement root;
public BaseComponent(WebElement root) {
this.root = root;
}
}
// Page Component Object
public class Product extends BaseComponent {
// The root element contains the entire component
public Product(WebElement root) {
super(root); // inventory_item
}
public String getName() {
// Locating an element begins at the root of the component
return root.findElement(By.className("inventory_item_name")).getText();
}
public BigDecimal getPrice() {
return new BigDecimal(
root.findElement(By.className("inventory_item_price"))
.getText()
.replace("$", "")
).setScale(2, RoundingMode.UNNECESSARY); // Sanitation and formatting
}
public void addToCart() {
root.findElement(By.id("add-to-cart-backpack")).click();
}
}
So now, the products test would use the page object and the page component object as follows.
public class ProductsTest {
@Test
public void testProductInventory() {
var productsPage = new ProductsPage(driver);
var products = productsPage.getProducts();
assertEquals(6, products.size()); // expected, actual
}
@Test
public void testProductPrices() {
var productsPage = new ProductsPage(driver);
// Pass a lambda expression (predicate) to filter the list of products
// The predicate or "strategy" is the behavior passed as parameter
var backpack = productsPage.getProduct(p -> p.getName().equals("Backpack"));
var bikeLight = productsPage.getProduct(p -> p.getName().equals("Bike Light"));
assertEquals(new BigDecimal("29.99"), backpack.getPrice());
assertEquals(new BigDecimal("9.99"), bikeLight.getPrice());
}
}
The page and component are represented by their own objects. Both objects only have methods for the services they offer, which matches the real-world application in object-oriented programming.
You can even nest component objects inside other component objects for more complex pages. If a page in the AUT has multiple components, or common components used throughout the site (e.g. a navigation bar), then it may improve maintainability and reduce code duplication.
Other Design Patterns Used in Testing
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.
Implementation Notes
PageObjects can be thought of as facing in two directions simultaneously. Facing toward the developer of a test, they represent the services offered by a particular page. Facing away from the developer, they should be the only thing that has a deep knowledge of the structure of the HTML of a page (or part of a page) It’s simplest to think of the methods on a Page Object as offering the “services” that a page offers rather than exposing the details and mechanics of the page. As an example, think of the inbox of any web-based email system. Amongst the services it offers are the ability to compose a new email, choose to read a single email, and list the subject lines of the emails in the inbox. How these are implemented shouldn’t matter to the test.
Because we’re encouraging the developer of a test to try and think about the services they’re interacting with rather than the implementation, PageObjects should seldom expose the underlying WebDriver instance. To facilitate this, methods on the PageObject should return other PageObjects. This means we can effectively model the user’s journey through our application. It also means that should the way that pages relate to one another change (like when the login page asks the user to change their password the first time they log into a service when it previously didn’t do that), simply changing the appropriate method’s signature will cause the tests to fail to compile. Put another way; we can tell which tests would fail without needing to run them when we change the relationship between pages and reflect this in the PageObjects.
One consequence of this approach is that it may be necessary to model (for example) both a successful and unsuccessful login; or a click could have a different result depending on the app’s state. When this happens, it is common to have multiple methods on the PageObject:
public class LoginPage {
public HomePage loginAs(String username, String password) {
// ... clever magic happens here
}
public LoginPage loginAsExpectingError(String username, String password) {
// ... failed login here, maybe because one or both of the username and password are wrong
}
public String getErrorMessage() {
// So we can verify that the correct error is shown
}
}
The code presented above shows an important point: the tests, not the PageObjects, should be responsible for making assertions about the state of a page. For example:
public void testMessagesAreReadOrUnread() {
Inbox inbox = new Inbox(driver);
inbox.assertMessageWithSubjectIsUnread("I like cheese");
inbox.assertMessageWithSubjectIsNotUnread("I'm not fond of tofu");
}
could be re-written as:
public void testMessagesAreReadOrUnread() {
Inbox inbox = new Inbox(driver);
assertTrue(inbox.isMessageWithSubjectIsUnread("I like cheese"));
assertFalse(inbox.isMessageWithSubjectIsUnread("I'm not fond of tofu"));
}
Of course, as with every guideline, there are exceptions, and one that is commonly seen with PageObjects is to check that the WebDriver is on the correct page when we instantiate the PageObject. This is done in the example below.
Finally, a PageObject need not represent an entire page. It may represent a section that appears frequently within a site or page, such as site navigation. The essential principle is that there is only one place in your test suite with knowledge of the structure of the HTML of a particular (part of a) page.
Summary
- The public methods represent the services that the page offers
- Try not to expose the internals of the page
- Generally don’t make assertions
- Methods return other PageObjects
- Need not represent an entire page
- Different results for the same action are modelled as different methods
Example
public class LoginPage {
private final WebDriver driver;
public LoginPage(WebDriver driver) {
this.driver = driver;
// Check that we're on the right page.
if (!"Login".equals(driver.getTitle())) {
// Alternatively, we could navigate to the login page, perhaps logging out first
throw new IllegalStateException("This is not the login page");
}
}
// The login page contains several HTML elements that will be represented as WebElements.
// The locators for these elements should only be defined once.
By usernameLocator = By.id("username");
By passwordLocator = By.id("passwd");
By loginButtonLocator = By.id("login");
// The login page allows the user to type their username into the username field
public LoginPage typeUsername(String username) {
// This is the only place that "knows" how to enter a username
driver.findElement(usernameLocator).sendKeys(username);
// Return the current page object as this action doesn't navigate to a page represented by another PageObject
return this;
}
// The login page allows the user to type their password into the password field
public LoginPage typePassword(String password) {
// This is the only place that "knows" how to enter a password
driver.findElement(passwordLocator).sendKeys(password);
// Return the current page object as this action doesn't navigate to a page represented by another PageObject
return this;
}
// The login page allows the user to submit the login form
public HomePage submitLogin() {
// This is the only place that submits the login form and expects the destination to be the home page.
// A seperate method should be created for the instance of clicking login whilst expecting a login failure.
driver.findElement(loginButtonLocator).submit();
// Return a new page object representing the destination. Should the login page ever
// go somewhere else (for example, a legal disclaimer) then changing the method signature
// for this method will mean that all tests that rely on this behaviour won't compile.
return new HomePage(driver);
}
// The login page allows the user to submit the login form knowing that an invalid username and / or password were entered
public LoginPage submitLoginExpectingFailure() {
// This is the only place that submits the login form and expects the destination to be the login page due to login failure.
driver.findElement(loginButtonLocator).submit();
// Return a new page object representing the destination. Should the user ever be navigated to the home page after submiting a login with credentials
// expected to fail login, the script will fail when it attempts to instantiate the LoginPage PageObject.
return new LoginPage(driver);
}
// Conceptually, the login page offers the user the service of being able to "log into"
// the application using a user name and password.
public HomePage loginAs(String username, String password) {
// The PageObject methods that enter username, password & submit login have already defined and should not be repeated here.
typeUsername(username);
typePassword(password);
return submitLogin();
}
}
Support in WebDriver
There is a PageFactory in the support package that provides support for this pattern and helps to remove some boiler-plate code from your Page Objects at the same time.
