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指南和建议

Selenium项目的一些测试指南和建议.

关于"最佳实践"的注解:我们有意在本文档中避免使用"最佳实践"的说辞. 没有一种方法可以适用于所有情况. 我们更喜欢"指南和建议"的想法. 我们鼓励您通读这些内容, 并仔细地确定哪种方法适用于您的特定环境.

由于许多原因, 功能测试很难正确完成. 即便应用程序的状态, 复杂性, 依赖还不够让测试变得 足够复杂, 操作浏览器(特别是跨浏览器的兼容性测试)就已经使得写一个好的测试变成一种挑战.

Selenium提供了一些工具使得功能测试用户更简单的操作浏览器, 但是这些工具并不能帮助你来写一个好的 架构的测试套件. 这章我们会针对怎么来做web页面的功能测试的自动化给出一些忠告, 指南和建议.

这章记录了很多历年来成功的使用Selenium的用户的常用的软件设计模式.

1 - PO设计模式

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.

2 - 领域特定语言

领域特定语言 (DSL) 是一种为用户提供解决问题的表达方式的系统. 它使用户可以按照自己的术语与系统进行交互, 而不仅仅是通过程序员的语言.

您的用户通常并不关心您网站的外观. 他们不在乎装饰, 动画或图形. 他们希望借助于您的系统, 以最小的难度使新员工融入整个流程; 他们想预订去阿拉斯加的旅行; 他们想以折扣价配置和购买独角兽. 您作为测试人员的工作应尽可能接近"捕捉”这种思维定势. 考虑到这一点, 我们开始着手"建模”您正在工作的应用程序, 以使测试脚本 (发布前用户仅有的代理) “说话”并代表用户.

在Selenium中, DSL通常由方法表示, 其编写方式使API简单易读-它们使开发人员和干系人 (用户, 产品负责人, 商业智能专家等) 之间能够产生汇报.

好处

  • 可读: 业务关系人可以理解.
  • 可写: 易于编写, 避免不必要的重复.
  • 可扩展: 可以 (合理地) 添加功能而无需打破约定以及现有功能.
  • 可维护: 通过将实现细节排除在测试用例之外, 您可以很好地隔离 AUT* 的修改.

Java

以下是Java中合理的DSL方法的示例. 为简便起见, 假定 driver 对象是预定义的并且可用于该方法.

/**
 * Takes a username and password, fills out the fields, and clicks "login".
 * @return An instance of the AccountPage
 */
public AccountPage loginAsUser(String username, String password) {
  WebElement loginField = driver.findElement(By.id("loginField"));
  loginField.clear();
  loginField.sendKeys(username);

  // Fill out the password field. The locator we're using is "By.id", and we should
  // have it defined elsewhere in the class.
  WebElement passwordField = driver.findElement(By.id("password"));
  passwordField.clear();
  passwordField.sendKeys(password);

  // Click the login button, which happens to have the id "submit".
  driver.findElement(By.id("submit")).click();

  // Create and return a new instance of the AccountPage (via the built-in Selenium
  // PageFactory).
  return PageFactory.newInstance(AccountPage.class);
}

此方法完全从测试代码中抽象出输入字段, 按钮, 单击甚至页面的概念. 使用这种方法, 测试人员要做的就是调用此方法. 这给您带来了维护方面的优势: 如果登录字段曾经更改过, 则只需更改此方法-而非您的测试.

public void loginTest() {
    loginAsUser("cbrown", "cl0wn3");

    // Now that we're logged in, do some other stuff--since we used a DSL to support
    // our testers, it's as easy as choosing from available methods.
    do.something();
    do.somethingElse();
    Assert.assertTrue("Something should have been done!", something.wasDone());

    // Note that we still haven't referred to a button or web control anywhere in this
    // script...
}

郑重强调: 您的主要目标之一应该是编写一个API, 该API允许您的测试解决 当前的问题, 而不是UI的问题. 用户界面是用户的次要问题–用户并不关心用户界面, 他们只是想完成工作. 您的测试脚本应该像用户希望做的事情以及他们想知道的事情的完整清单那样易于阅读. 测试不应该考虑UI如何要求您去做.

*AUT: 待测系统

3 - 生成应用程序状态

Selenium不应用于准备测试用例. 测试用例中所有重复性动作和准备工作, 都应通过其他方法来完成.
例如, 大多数Web UI都具有身份验证 (诸如一个登录表单) . 在每次测试之前通过Web浏览器进行登录的消除, 将提高测试的速度和稳定性. 应该创建一种方法来获取对 AUT* 的访问权限 (例如, 使用API登录并设置Cookie) . 此外, 不应使用Selenium创建预加载数据来进行测试的方法.
如前所述, 应利用现有的API为 AUT* 创建数据. *AUT: 待测系统

4 - 模拟外部服务

消除对外部服务的依赖性将大大提高测试的速度和稳定性.

5 - 改善报告

Selenium并非旨在报告测试用例的运行状态. 利用单元测试框架的内置报告功能是一个好的开始. 大多数单元测试框架都有可以生成xUnit或HTML格式的报告. xUnit报表很受欢迎, 可以将其结果导入到持续集成(CI)服务器, 例如Jenkins、Travis、Bamboo等. 以下是一些链接, 可获取关于几种语言报表输出的更多信息.

NUnit 3 Console Runner

NUnit 3 Console Command Line

xUnit getting test results in TeamCity

xUnit getting test results in CruiseControl.NET

xUnit getting test results in Azure DevOps

6 - 避免共享状态

尽管在多个地方都提到过, 但这点仍值得被再次提及. 确保测试相互隔离.

  • 不要共享测试数据. 想象一下有几个测试, 每个测试都会在选择操作执行之前查询数据库中的有效订单. 如果两个测试采用相同的顺序, 则很可能会出现意外行为.

  • 清理应用程序中过时的数据, 这些数据可能会被其他测试. 例如无效的订单记录.

  • 每次测试都创建一个新的WebDriver实例. 这在确保测试隔离的同时可以保障并行化更为简单.

7 - 使用定位器的提示

何时使用哪些定位器以及如何在代码中最好地管理它们.

这里有一些 支持的定位策略 的例子 .

一般来说,如果 HTML 的 id 是可用的、唯一的且是可预测的,那么它就是在页面上定位元素的首选方法。它们的工作速度非常快,可以避免复杂的 DOM 遍历带来的大量处理。

如果没有唯一的 id,那么最好使用写得好的 CSS 选择器来查找元素。XPath 和 CSS 选择器一样好用,但是它语法很复杂,并且经常很难调试。尽管 XPath 选择器非常灵活,但是他们通常未经过浏览器厂商的性能测试,并且运行速度很慢。

基于链接文本和部分链接文本的选择策略有其缺点,即只能对链接元素起作用。此外,它们在 WebDriver 内部调用 querySelectorAll 选择器。

标签名可能是一种危险的定位元素的方法。页面上经常出现同一标签的多个元素。这在调用 findElements(By) 方法返回元素集合的时候非常有用。

建议您尽可能保持定位器的紧凑性和可读性。使用 WebDriver 遍历 DOM 结构是一项性能花销很大的操作,搜索范围越小越好。

8 - 测试的独立性

将每个测试编写为独立的单元. 以不依赖于其他测试完成的方式编写测试:

例如有一个内容管理系统, 您可以借助其创建一些自定义内容, 这些内容在发布后作为模块显示在您的网站上, 并且CMS和应用程序之间的同步可能需要一些时间.

测试模块的一种错误方法是在测试中创建并发布内容, 然后在另一测试中检查该模块. 这是不可取的, 因为发布后内容可能无法立即用于其他测试.

与之相反的事, 您可以创建在受影响的测试中打开和关闭的打桩内容, 并将其用于验证模块. 而且, 对于内容的创建, 您仍然可以进行单独的测试.

9 - 考虑使用Fluent API

Martin Fowler创造了术语 “Fluent API”. Selenium已经在其 FluentWait 类中实现了类似的东西, 这是对标准 Wait 类的替代. 您可以在页面对象中启用Fluent API设计模式, 然后使用如下代码段查询Google搜索页面:

driver.get( "http://www.google.com/webhp?hl=en&amp;tab=ww" );
GoogleSearchPage gsp = new GoogleSearchPage(driver);
gsp.setSearchString().clickSearchButton();

Google页面对象类具有这种流畅行为后可能看起来像这样:

public abstract class BasePage {
    protected WebDriver driver;

    public BasePage(WebDriver driver) {
        this.driver = driver;
    }
}

public class GoogleSearchPage extends BasePage {
    public GoogleSearchPage(WebDriver driver) {
        super(driver);
        // Generally do not assert within pages or components.
        // Effectively throws an exception if the lambda condition is not met.
        new WebDriverWait(driver, Duration.ofSeconds(3)).until(d -> d.findElement(By.id("logo")));
    }

    public GoogleSearchPage setSearchString(String sstr) {
        driver.findElement(By.id("gbqfq")).sendKeys(sstr);
        return this;
    }

    public void clickSearchButton() {
        driver.findElement(By.id("gbqfb")).click();
    }
}

10 - 每次测试都刷新浏览器

每次测试都从一个干净的已知状态开始. 理想情况下, 为每次测试打开一个新的虚拟机. 如果打开新虚拟机不切实际, 则至少应为每次测试启动一个新的WebDriver. 对于Firefox, 请使用您已知的配置文件去启动WebDriver. 大多数浏览器驱动器,像GeckoDriver和ChromeDriver那样,默认都会以干净的已知状态和一个新的用户配置文件开始。

WebDriver driver = new FirefoxDriver();