Mastering Assertions in TestNG

Introduction

Assertions in TestNG serve as powerful tools for validating expected outcomes in automated test scripts. By incorporating assertions, developers and testers can ensure that the application behaves as intended during various scenarios. TestNG provides a robust framework for implementing assertions, offering a wide range of methods to verify conditions and streamline the testing process.

Assertions in TestNG

Assertions in TestNG are a way to verify that the expected result and the actual result matched or not. An example of assertion can be logging into the website, checking the title of the webpage, verifying the functionality of an input box that takes only integers, etc.

We should remember that an assertion in TestNG is successful only if there are no exceptions thrown during the test case execution.

Syntax for TestNG Assertions

import org.testng.Assert;

public class AssertionExample {

    public void testStringEquality() {
        String actual = "Hello, TestNG";
        String expected = "Hello, TestNG";

        // Assertion using TestNG
        Assert.assertEquals(actual, expected, "String equality check failed");
    }
}

In this example, the assertEquals method is used to verify if the actual string matches the expected string. If not, an error message ("String equality check failed") will be displayed.

How to Use Assertions in TestNG

import org.testng.Assert;

public class AssertionExample {

    public void testNumericInequality() {
        int actual = 10;
        int expected = 5;

        // Assertion using TestNG
        Assert.assertNotEquals(actual, expected, "Numeric inequality check failed");
    }
}

In this example, assertNotEquals is used to ensure that the actual numeric value is not equal to the expected value. If the assertion fails, the specified error message ("Numeric inequality check failed") will be displayed.

Using Messages as a Parameter in TestNG Asserts

Adding a custom message to your assertions can significantly improve the clarity of your test reports. Let's enhance our previous example:

import org.testng.Assert;

public class AssertionExample {

    public void testArrayEquality() {
        int[] actualArray = {1, 2, 3};
        int[] expectedArray = {1, 2, 3};

        // Assertion using TestNG with a custom message
        Assert.assertEquals(actualArray, expectedArray, "Array equality check failed");
    }
}

Types of Asserts in TestNG

There are two types of Assert

Hard Assert :

It stops the test execution when an assert statement fails, and the subsequent assert statements are therefore not validated. Hard asserts are the default type of asserts in TestNG

 import org.testng.Assert;
 import org.testng.annotations.Test;

 public class HardAssertExample {

     @Test
     public void testLogin() {
         // Perform login
         boolean loginSuccessful = performLogin("username", "password");

         // Hard Assertion
         Assert.assertTrue(loginSuccessful, "Login failed");

         // Subsequent statements executed only if login is successful
         // Perform other actions after successful login
     }

     private boolean performLogin(String username, String password) {
         // Implementation of login logic
         // Return true if login is successful, false otherwise
         return true;
     }
 }

Soft Assert :

It is the opposite of hard asserts where the subsequent assertions keep on running even though one assert validation fails, i.e., the test execution does not stop. To use this, you need to include the package org.testng.asserts.Softassert.

 import org.testng.asserts.SoftAssert;
 import org.testng.annotations.Test;

 public class SoftAssertExample {

     @Test
     public void testProductDetails() {
         SoftAssert softAssert = new SoftAssert();

         // Check product details
         softAssert.assertEquals(getProductName(), "Laptop", "Incorrect product name");
         softAssert.assertEquals(getProductPrice(), 1200, "Incorrect product price");
         softAssert.assertTrue(isProductInStock(), "Product out of stock");

         // Mark test as failed if any soft assertion fails
         softAssert.assertAll();
     }

     private String getProductName() {
         // Implementation to retrieve product name
         return "Laptop";
     }

     private int getProductPrice() {
         // Implementation to retrieve product price
         return 1200;
     }

     private boolean isProductInStock() {
         // Implementation to check if the product is in stock
         return true;
     }
 }

Difference: Hard Asserts vs Soft Asserts

Feature	Hard Asserts	Soft Asserts
Behavior on Failure	Stops test execution	Continues test execution
Reporting Multiple Failures	Reports only the first failure	Reports all failures at once
Continuation after Failure	Does not continue after failure	Continues after each assertion, even if previous ones fail
Syntax	`Assert.assertEquals(actual, expected, message)`	`SoftAssert softAssert = new SoftAssert();softAssert.assertEquals(actual, expected, message)`
Usage	Ideal for critical validations where further test steps are dependent on the success of the current one.	Suitable when you want to collect multiple assertions within a test without stopping at the first failure. Useful for scenarios where you want to capture all possible issues before terminating the test.

Commonly Used TestNG Assert Methods

//assertEquals: Verifies that two values are equal.
Assert.assertEquals(actual, expected, "Assertion Failure Message"); 

//assertNotEquals: Verifies that two values are not equal.
Assert.assertNotEquals(actual, expected, "Assertion Failure Message"); 

//assertTrue: Verifies that the provided condition is true.
Assert.assertTrue(condition, "Assertion Failure Message"); 

//assertFalse: Verifies that the provided condition is false.
Assert.assertFalse(condition, "Assertion Failure Message"); 

//assertNull: Verifies that the provided object reference is null.
Assert.assertNull(object, "Assertion Failure Message"); 

//assertNotNull: Verifies that the provided object reference is not null.
Assert.assertNotNull(object, "Assertion Failure Message"); 

//assertThrows: Verifies that a specific exception is thrown during the execution of a test.
Assert.assertThrows(Exception.class, () -> { 
Code that should throw the specified exception
},"Assertion Failure Message");

Conclusion

In conclusion, leveraging TestNG assertions enhances the reliability and effectiveness of test suites, enabling prompt identification of discrepancies in application behavior. By systematically incorporating assertions into test scripts, developers can achieve more accurate and dependable testing results, ultimately contributing to the overall quality and stability of the software under examination.