Expected Exceptions in TestNG

  

What is Expected Exceptions in TestNG?

In TestNG, expected exceptions are used to verify that a method throws a specific exception during execution. This is useful when you're testing error-handling logic in your application.

If the specified exception is thrown, the test passes. If not (either no exception or a different one), the test fails.

Syntax:

You use expectedExceptions inside the @Test annotation:

@Test(expectedExceptions = ExceptionType.class)
public void testMethod() {
    // code that should throw ExceptionType
}

Example:

Let’s say you want to test whether a method throws an ArithmeticException when dividing by zero:

import org.testng.annotations.Test;

public class ExpectedExceptionExample {

    @Test(expectedExceptions = ArithmeticException.class)
    public void testDivideByZero() {
        int result = 10 / 0; // This will throw ArithmeticException
    }

    @Test
    public void testNoException() {
        int result = 10 / 2;
        System.out.println("Result: " + result); // This will not throw an exception
    }
}

Explanation:

• testDivideByZero() is expected to throw ArithmeticException. Since dividing by 0 does throw it, the test passes.

• testNoException() runs normally and also passes, as it's not expecting any exception.

Expected exceptions are useful for negative testing, such as:

• Handling of null inputs

• Invalid configurations

• Divisions by zero

• Custom business exceptions