11 Essential Selenium Interview Questions *

To wait for a page to load, explicit wait can be used. Explicit waits stall until some specific condition is met. Although Thread.Sleep() 是一种显式等待的形式，线程在特定的时间内停止, 等待页面加载可能不是最可靠的方式.

For example, rather than using something like:

Thread.Sleep(30000);

当线程休眠30秒(30,000毫秒)时，可以使用以下方法:

WebDriverWait wait= new WebDriverWait(webDriver,30);
wait.until(ExpectedConditions.visibilityOf(h1));

其中Selenium等待，直到给定的元素在页面上可见, or throws TimeoutException after waiting for 30 seconds.

Selenium中的页面对象模型是一种使用类来表示网页的设计模式. 类中的变量可以用来保存对网页上元素的引用, and methods can be used to implement behaviors. 这允许以一种优雅的方式实现既可读又易于维护和扩展的测试例程.

clickLoginButton();
setCredentials(user_name, user_password);
submitLoginForm();

页面工厂用于初始化每个WebElement变量，并使用配置的“定位器”将其引用到实际网页上的相应元素。. Annotations, such as @FindBy, can be used to define strategies for looking up elements, along with the necessary information for identifying them:

@FindBy(how=How.NAME, using="username")
private WebElement user_name;

More about Page Object Model and Page Factory can be found here.

为了操作框架及其内容，您必须首先切换到它. 这类似于你必须切换到不同的页面才能与之交互:

driver.switchTo().frame(index);

… where index is the zero-based index of the frame. 切换帧将所有进一步的交互通过驱动程序指向选定的帧. The frame 方法也适用于名称、元素ID和对已定位元素的引用.

To switch back to the default frame, the defaultContent method can be used:

driver.switchTo().defaultContent();

• CSS selectors are often easier to read than XPath. 大多数前端开发人员可能已经很熟悉CSS选择器了.

• 对CSS选择器的支持在各种现代web浏览器中是相当一致的, which is not the case with their XPath engines.

• CSS selectors work faster than XPath.

For various reasons, such as the ones outlined above, Selenium“最佳实践”建议使用CSS选择器而不是XPath.

Immediate child:

An immediate child in XPath is defined indicated using “/”, while on CSS, it is indicated using “>”. For example, with XPath:

//div/p

… and with CSS:

div > p

Descendent:

查找任何div元素(i.e. 段落元素出现在以div元素为根的子树中), we can use “//” in XPath, and just a whitespace in CSS:

//div//p

div p

It defines a variable sample of type WebElement, 并使用XPath搜索用一个包含文本值“data”的元素的引用来初始化它。.

这可以通过在聚焦的元素上模拟按键来实现. One way is to perform “actions” on the web driver object:

new Actions(webDriver).sendKeys(“some text”).perform();

另一种方法是先切换到活动元素，然后直接向它发送密钥:

webDriver.switchTo().activeElement().sendKeys(“some text”);

无头驱动通常用于持续集成(CI)设置. Headless drivers, such as PhantomJS, provide all standard web browser functionalities, but run in the command-line. 这些驱动程序基于命令行工具，不产生屏幕输出, making them ideal for completely automated setups.

To be able to visually investigate test failures, 开发人员需要实现捕获屏幕截图的机制, otherwise rely on command line output.

就网页而言，绝对xpath从根元素开始:

html/head/body/table/tbody/tr/th

Relative XPaths, on the other hand, usually start with “//”:

//table/tbody/tr/th 

尽管这两个xpath可能都引用某个网页上的相同元素, 前者更有可能因对页面所做的任何更改而中断. For example, 将表移动到div元素内部将使绝对XPath无法定位该元素. 另一方面，相对XPath仍将继续工作.

混合框架是关键字驱动框架和数据驱动框架的组合.

它是当被调用的元素由于任何原因不再附加到DOM时引发的异常.