Assertions in TestNG are a way to verify that the expected result and the actual result matches or not in the test case. A test is considered successful ONLY if it is completed without throwing any exception. 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.
Below are few commonly used assertions in TestNG.
1. Assert.assertEquals(String actual, String expected) – It takes two string arguments and checks whether both strings are equal or not. If they are not, it will fail the test and an AssertionError is thrown.
2. Assert.assertEquals(String actual, String expected, String message) – It takes two string arguments and checks whether both strings are equal or not. If they are not, it will fail the test and an AssertionError is thrown with message provided as argument.
3. Assert.assertEquals(boolean actual, boolean expected) – It takes two Boolean arguments and checks whether both are equal or not. If they are not, it will fail the test and an AssertionError is thrown.
4. Assert.assertEquals(java.util.Collection actual, java.util.Collection expected, java.lang.String message) – It takes two collection objects and verifies both collections contain the same elements and with the same order. If they are not, it will fail the test and an AssertionError is thrown.
5. Assert.assertTrue(condition) – It takes one boolean argument and checks that a condition is true or not. If not, it will fail the test and an AssertionError is thrown.
6. Assert.assertTrue(condition, message) – It takes one boolean argument and checks that a condition is true or not. If not, it will fail the test and an AssertionError is thrown with message provided as argument.
7. Assert.assertFalse(condition) – It takes one boolean argument and checks that a condition is false or not. If not, it will fail the test and an AssertionError is thrown.
8. Assert.assertFalse(condition, message) – It takes one boolean argument and checks that a condition is false or not. If not, it will fail the test and an AssertionError is thrown with message provided as argument.
9. Assert.assertSame(String actual, String expected) – It asserts that two objects refer to the same object. If they do not, an AssertionError is thrown.
10. Assert.assertNotSame(String actual, String expected) – It asserts that two objects do not refer to the same object. If they do, an AssertionError is thrown.
import org.testng.Assert;
import org.testng.annotations.Test;
public class TestNGAssertionDemo {
@Test
public void testAssertions() {
// test data
String str1 = new String("TestNG");
String str2 = new String("TestNG");
String str3 = null;
String str4 = "TestNG";
String str5 = "TestNG";
String str6 = new String("Not_TestNG");
int val1 = 5;
int val2 = 6;
// Check that two objects are equal
Assert.assertEquals(str1, str2);
System.out.println("Equals Assertion is successful");
// Check that two objects are not equal
Assert.assertNotEquals(str1, str6);
System.out.println("NotEquals Assertion is successful");
// Check that a condition is true
Assert.assertTrue(val1 < val2);
System.out.println("True Assertion is successful");
// Check that a condition is false
Assert.assertFalse(val1 > val2);
System.out.println("False Assertion is successful");
// Check that an object isn't null
Assert.assertNotNull(str1);
System.out.println("Not Null Assertion is successful");
// Check that an object is null
Assert.assertNull(str3);
// Check if two object references point to the same object
Assert.assertSame(str4, str5);
System.out.println("Same Assertion is successful");
// Check if two object references not point to the same object
Assert.assertNotSame(str1, str3);
System.out.println("Not Same Assertion is successful");
}
}
Output
Equals Assertion is successful
NotEquals Assertion is successful
True Assertion is successful
False Assertion is successful
Not Null Assertion is successful
Same Assertion is successful
Not Same Assertion is successful
Lets see if an assertion fails, how the output looks shown below. In the below example, we are verifying the pageTitle of Gmail. If the test fails, we should see the message provided in the assertion also.
import org.openqa.selenium.WebDriver;
importorg.openqa.selenium.firefox.FirefoxDriver;
import org.testng.Assert;
import org.testng.annotations.Test;
public class TestNGAssertionFailureDemo {
@Test
public void AssertionFailure() throws InterruptedException {
System.setProperty("webdriver.gecko.driver", "src\\test\\resources\\webdrivers\\window\\geckodriver.exe");
WebDriver driver = new FirefoxDriver();
// Test Condition 1: If Page title matches with actualTitle then it finds email
// title and enters the value which we pass
driver.get("https://www.gmail.com");
String actualTitle = "Google";
String expectedTitle = driver.getTitle();
Assert.assertEquals(expectedTitle, actualTitle, "Incorrect page title");
}
}
Output
FAILED: AssertionFailure
java.lang.AssertionError: Incorrect page title expected [Google] but found [Gmail]
You can show in the output console, there is an error message “Incorrect page title” as we have mentioned this message in the Assertion.
QA Automation Expert 
Nice explanation
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Good job
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