Synchronization in Selenium Webdriver

It is a mechanism which involves more than one components to work parallel with Each other.

Generally in Test Automation, we have two components
1. Application Under Test
2. Test Automation Tool.

Both these components will have their own speed. We should write our scripts in such a way that both the components should move with same and desired speed, so that we will not encounter "Element Not Found" errors which will consume time again in debugging.

Synchronization can be classified into two categories:

1. Unconditional 
2. Conditional Synchronization

Unconditional :
In this we just specify timeout value only. We will make the tool to wait until certain amount of time and then proceed further.

Examples: Wait() and Thread.Sleep();

The main disadvantage for the above statements are, there is a chance of unnecessary waiting time even though the application is ready.

The advantages are like in a situation where we interact for third party systems like interfaces, it is not possible to write a condition or check for a condition. Here in this situations, we have to make the application to wait for certain amount of time by specifying the timeout value.

Conditional Synchronization:

We specify a condition along with timeout value, so that tool waits to check for the condition and then come out if nothing happens.

It is very important to set the timeout value in conditional synchronization, because the tool should proceed further instead of making the tool to wait for a particular condition to satisfy.

In Selenium we have implicit Wait and Explicit Wait conditional statements. Check here for Examples on how to use Webdriver Waits

1. Implicit Wait.

An implicit wait is to tell WebDriver to poll the DOM for a certain amount of time when trying to find an element or elements if they are not immediately available.

The default setting is 0. Once when we define the implicit wait, it will set for the life of the WebDriver object instance.

It is a mechanism which will be written once and applied for entire session automatically. It should be applied immediately once we initiate the Webdriver.

Implicit wait will not work all the commands/statements in the application. It will work only for "FindElement" and "FindElements" statements.

If we set implicit wait, find element will not throw an exception if the element is not found in first instance, instead it will poll for the element until the timeout and then proceeds further. We should always remember to add the below syntax immediately below the Webdriver statement.

Syntax:

driver.manage.TimeOuts.implicitwait(6,Timeunit.SECONDS);

Example using implicit timeout

WebDriver driver = new FirefoxDriver();
driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);
driver.get("http://www.google.com");

Explicit Wait:

We need to define a wait statement for certain condition to be satisfied until the specified timeout period. If the Webdriver finds the element within the timeout period the code will get executed.

Explicit wait is mostly used when we need to Wait for a specific content/attribute change after performing any action, like when application gives AJAX call to system and get dynamic data and render on UI.

Example: Like there are drop-downs Country and State, based on the country value selected, the values in the state drop-down will change, which will take few seconds of time to get the data based on user selection.

Example:

/*Explicit wait for state dropdown field*/
    WebDriverWait wait = new WebDriverWait(driver, 10);
    wait.until(ExpectedConditions.visibilityOfElementLocated(By.id("statedropdown")));

The above statement waits up to 10 seconds before throwing Exception (TimeoutException - Timed out after 10 seconds waiting for visibility of element) or if it finds the element, it will return in 0 - 10 seconds.

There are different waits that can be used based on the needs which we frequently come across when automating web applications. Check here for WebDriver Waits Example.

Fluent Wait:

Using FluentWait we can define the maximum amount of time to wait for a condition, as well as the frequency with which to check for the condition.

And also the user can configure to ignore specific types of exceptions such as "NoSuchElementExceptions" when searching for an element. NoSuchElement exception is thrown by findElement(By) and findElements(By). When ever it try to find any element it returns the first matching element on the current page else it throws NoSuchElementException - when no matching elements are found.

Syntax:

 
Wait<WebDriver> wait = new FluentWait<WebDriver>(driver)
     //Wait for the condition
           .withTimeout(30, TimeUnit.SECONDS) 
             // which to check for the condition with interval of 5 seconds. 
           .pollingEvery(5, TimeUnit.SECONDS) 
         //Which will ignore the NoSuchElementException
           .ignoring(NoSuchElementException.class);