JUnit Annotations Tutorial with Example: What is @Test and @After (2023)

With the knowledge of annotations in Junit5, one can easily learn and implement a JUnit test. Below is the important and frequently used JUnit annotations list:

In this tutorial, you will learn-

• JUnit Annotations Example
• JUnit Assert Class
• JUnit Test Cases Class
• JUnit TestResult Class
• JUnit Test Suite Class

JUnit Annotations Example

Let’s create a class covering important JUnit annotations with simple print statements and execute it with a test runner class:

Step 1) Consider below java class having various methods which are attached to above-listed annotations:

JunitAnnotationsExample.java

package guru99.junit;import static org.junit.Assert.assertEquals;import static org.junit.Assert.assertFalse;import java.util.ArrayList;import org.junit.After;import org.junit.AfterClass;import org.junit.Before;import org.junit.BeforeClass;import org.junit.Ignore;import org.junit.Test;public class JunitAnnotationsExample { private ArrayList<String> list; @BeforeClass public static void m1() { System.out.println("Using @BeforeClass , executed before all test cases "); } @Before public void m2() { list = new ArrayList<String>(); System.out.println("Using @Before annotations ,executed before each test cases "); } @AfterClass public static void m3() { System.out.println("Using @AfterClass ,executed after all test cases"); } @After public void m4() { list.clear(); System.out.println("Using @After ,executed after each test cases"); } @Test public void m5() { list.add("test"); assertFalse(list.isEmpty()); assertEquals(1, list.size()); } @Ignore public void m6() { System.out.println("Using @Ignore , this execution is ignored"); } @Test(timeout = 10) public void m7() { System.out.println("Using @Test(timeout),it can be used to enforce timeout in JUnit4 test case"); } @Test(expected = NoSuchMethodException.class) public void m8() { System.out.println("Using @Test(expected) ,it will check for specified exception during its execution"); }}

Step 2) let’s create a test runner class to execute above test:

TestRunner.java

package guru99.junit;import org.junit.runner.JUnitCore;import org.junit.runner.Result;import org.junit.runner.notification.Failure;public class TestRunner {public static void main(String[] args) { Result result = JUnitCore.runClasses(JunitAnnotationsExample.class);for (Failure failure : result.getFailures()) { System.out.println(failure.toString()); } System.out.println("Result=="+result.wasSuccessful()); }} 

Expected Result

• All the test cases will be executed one by one, and all print statement can be seen on a console.
• As discussed in above table @Before annotation in JUnit, @BeforeClass [ method m1() and m2() ] will be executed before each and before all test cases respectively.
• In the same way @After in JUnit, @afterClass (method m3() and m4()) will be executed after each and after all test cases respectively. @ignore (method m6())will be treated as ignoring the test.

Let’s analyse test cases used in above java class in detail:

1. Consider method m5() as given below :

@Test public void m5() { list.add("test"); assertFalse(list.isEmpty()); assertEquals(1, list.size()); }

In above method as you are adding a string in the variable “list” so

• list.isEmpty() will return false.
• assertFalse(list.isEmpty()) must return true.
• As a result, the test case will pass.

As you have added only one string in the list, so the size is one.

• list.size() must return int value as “1” .
• So assertEquals(1, list.size()) must return true.
• As a result, the test case will pass.

2. Consider method m7() as given below :

@Test(timeout = 10) public void m7() { System.out.println("Using @Test(timeout),it can be used to enforce timeout in JUnit4 test case"); }

As discussed above @Test(timeout = 10)annotation is used to enforce timeout in the test case.

3. Consider method m8() as given below :

@Test(expected = NoSuchMethodException.class) public void m8() { System.out.println("Using @Test(expected) ,it will check for specified exception during its execution"); }

As discussed above @Test(expected) will check for specified exception during its execution so method m8() will throw “No Such Method Exception.” As a result, the test will be executed with an exception.

As all test cases are passed, this results in a successful test execution.

Actual Result

As there are three test cases in above example, all test cases will be executed one by one. See output below:

JUnit Annotations Example

See below print statements which can be seen on console:

Using @BeforeClass , executed before all test cases

Using @Before annotations, executed before each test cases

Using @After, executed after each test cases

Using @Before annotations, executed before each test cases

Using @Test(timeout),it can be used to enforce timeout in JUnit4 test case

Using @After, executed after each test cases

Using @Before annotations, executed before each test cases

Using @Test(expected) ,it will check for specified exception during its execution

Using @After, executed after each test cases

Using @AfterClass, executed after all test cases

JUnit Assert Class

This class provides a bunch of assertion methods useful in writing a test case. If all assert statements are passed, test results are successful. If any assert statement fails, test results are failed.

As you seen earlier, below table describes important Assert methods and description:

JUnit Test Cases Class

To run multiple test, TestCase class is available in org.junit.TestCase packages. @Test annotation tells JUnit that this public void method (Test Case here) to which it is attached can be run as a test case.

Below table shows some important methods available in org.junit.TestCase class:

JUnit TestResult Class

When you execute a test, it returns a result (in the form of TestResult object). This TestResult object can be used to analyse the resultant object. This test result can be either failure or successful.
See below table for important methods used in org.junit.TestResult class:

JUnit Test Suite Class

If you want to execute multiple tests in a specified order, it can be done by combining all the tests in one place. This place is called as the test suites.

See below table for important methods used in org.junit.TestSuite class:

Summary:

• JUnit provides a portable API, which provides all important classes and Selenium annotations useful in writing a unit test.
• Classes which are very useful while writing a test case
  • org.junit.Assert
  • org.junit.TestCase
  • org.junit.TestResult
  • org.junit.TestSuite
• Important and frequently used JUnit annotations list@Before@BeforeClass@After

  @AfterClass

  @Test

  @Ignore