Handling Exceptions Using Exception Handling Framework in Selenium Scripts – Selenium Tutorial #19

In last WebDriver tutorial, we learned about 3 different types of important web elements like Web Tables, Frames and Dynamic elements and their handling mechanisms in selenium script

Before moving ahead with Framework tutorials in this Selenium training series, here in this tutorial we will learn about types of exceptions and how to handle exceptions in Java and Selenium scripts. Developers/testers use exception handling framework to handle an exception in selenium scripts.

Example: When selenium script fails due to the wrong locator, then the developer should be able to understand the reason for failure and this can be achieved easily if the exception is handled properly in the program.

Below we have described the types of exceptions and the different ways how we can use exception handling framework in selenium scripts.

Exceptions are events due to which java program ends abruptly without giving expected output. Java provides a framework where a user can handle exceptions.

There are three kinds of exceptions:

  1. Checked Exception
  2. Unchecked Exception
  3. Error

The class hierarchy of exception and error:

#1) Checked Exception: Checked exception is handled during compile time and it gives the compilation error if it is not caught and handled during compile time.

Example: FileNotFoundException, IOException etc.

#2) Unchecked Exception: In case of the unchecked exception, a compiler does not mandate to handle. The compiler ignores during compile time.

Example: ArrayIndexoutOfBoundException

#3) Error: When a scenario is fatal and the program cannot recover then JVM throws an error. Errors cannot be handled by the try-catch block. Even if the user tries to handle the error by using Try catch block, it cannot recover from the error.

Example: Assertion error, OutOfMemoryError etc.

Exception handling:

Try and Catch block:

try-catch blocks are generally used to handle exceptions. Type of exceptions is declared in catch block which is expected to come. When an exception comes in try block, immediately control moves to catch block.

Example:


try {
    br = new BufferedReader(new FileReader("Data"));
    } catch(IOException ie)
    {
         ie.printStackTrace();
    }

There can be multiple catch blocks for one try block depending upon the type of exception.

Example:




try {
    br = new BufferedReader(new FileReader("Data"));
    } catch(IOException ie)
    {
      ie.printStackTrace();
    } catch(FileNotFoundException file){
      file.printStackTrace();
    }

throws Exception:

throws keyword in java is used to throw an exception rather than handling it. All checked exceptions can be thrown by methods.

Example:


public static void main(String[] args) throws IOException
{
BufferedReader br=new BufferedReader(new FileReader("Data"));
     while ((line = br.readLine()) != null)
         {
           System.out.println(line);
         }
}

finally block:

finally, block executes irrespective of execution of try-catch block and it executes immediately after try/catch block completes.

Basically file close, database connection etc. can be closed in finally block.

Example:


try {
    br = new BufferedReader(new FileReader("Data"));
    } catch(IOException ie)
    {
      ie.printStackTrace();
    }
Finally {
          br.close();
        }

In the above example, BufferReader stream is closed in finally block. br.close() will always execute irrespective of execution of try and catch block.

Note: finally block can exist without any catch block. It is not necessary to have a catch block always.

There can be many catch blocks but only one finally block can be used.

Throwable: Throwable is parent class for error and exception. Generally it is difficult to handle errors in java. If a programmer is not sure about the type of error and exception, then it is advised to use the Throwable class which can catch both error and exception.

Example:


try {
   br = new BufferedReader(new FileReader("Data"));
     } catch (Throwable t)
     {
       t.printStackTrace();
     }

Exceptions in Selenium WebDriver:

Selenium has its own set of exceptions. While developing selenium scripts, a programmer has to handle or throw those exceptions. Below are few examples of exceptions in selenium.

Examples:

ElementNotVisibleException: If selenium tries to find an element but element is not visible within page

NoAlertPresentException: If a user tries to handle an alert box but the alert is not present.

NoSuchAttributeException: While trying to get attribute value but the attribute is not available in DOM.

NoSuchElementException: This exception is due to accessing an element which is not available on the page.

WebDriverException: Exception comes when a code is unable to initialize WebDriver.

Conclusion:

Exception handling is the essential part of every java program as well as selenium script. We can build robust and optimal code by handling an exception in smart ways. And it is also a best practice to handle exceptions in a script which will give you a better report when a program fails due to any reason.

Here we have tried to cover the process and framework of exception handling which is required to be implemented in selenium scripts.

Remember it is not mandatory to always handle the exception in a try-catch block. You can also throw an exception depending upon the requirement in a script.

Next Tutorial #20: In the upcoming tutorial, we would discuss about the various types of testing frameworks available. We would also study about the pros and cons of using a fledged framework approach in automation testing. We would discuss in detail about the Test data driven framework.

Please post your queries, related to handling exception in Selenium WebDriver, if you have any.