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

What is JUnit Annotations?

JUnit Annotations is a special form of syntactic meta-data that can be added to Java source code for better code readability and structure. Variables, parameters, packages, methods and classes can be annotated. Annotations were introduced in Junit4, which makes Java code more readable and simple. This is the big difference between Junit3 and Junit4 that Junit4 is annotation based.

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:

S.No.	Annotations	Description
1.	@Test	This annotation is a replacement of org.junit.TestCase which indicates that public void method to which it is attached can be executed as a test Case.
2.	@Before	This annotation is used if you want to execute some statement such as preconditions before each test case.
3.	@BeforeClass	This annotation is used if you want to execute some statements before all the test cases for e.g. test connection must be executed before all the test cases.
4.	@After	This annotation can be used if you want to execute some statements after each Test Case for e.g resetting variables, deleting temporary files ,variables, etc.
5.	@AfterClass	This annotation can be used if you want to execute some statements after all test cases for e.g. Releasing resources after executing all test cases.
6.	@Ignores	This annotation can be used if you want to ignore some statements during test execution for e.g. disabling some test cases during test execution.
7.	@Test(timeout=500)	This annotation can be used if you want to set some timeout during test execution for e.g. if you are working under some SLA (Service level agreement), and tests need to be completed within some specified time.
8.	@Test(expected=IllegalArgumentException.class)	This annotation can be used if you want to handle some exception during test execution. For, e.g., if you want to check whether a particular method is throwing specified exception or not.

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:

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.

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.

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:

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:

S.No.	Method	Description
1.	void assertEquals(boolean expected, boolean actual)	It checks whether two values are equals similar to equals method of Object class
2.	void assertFalse(boolean condition)	functionality is to check that a condition is false.
3.	void assertNotNull(Object object)	“assertNotNull” functionality is to check that an object is not null.
4.	void assertNull(Object object)	“assertNull” functionality is to check that an object is null.
5.	void assertTrue(boolean condition)	“assertTrue” functionality is to check that a condition is true.
6.	void fail()	If you want to throw any assertion error, you have fail() that always results in a fail verdict.
7.	void assertSame([String message]	“assertSame” functionality is to check that the two objects refer to the same object.
8.	void assertNotSame([String message]	“assertNotSame” functionality is to check that the two objects do not refer to the same object.

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:

S.No.	Method	Description
1.	int countTestCases()	This method is used to count how many number of test cases executed by run(TestResult tr) method.
2.	TestResult createResult()	This method is used to create a TestResult object.
3.	String getName()	This method returns a string which is nothing but a TestCase.
4.	TestResult run()	This method is used to execute a test which returns a TestResult object
5.	void run(TestResult result)	This method is used to execute a test having a TestResult object which doesn’t returns anything.
6.	void setName(String name)	This method is used to set a name of a TestCase.
7.	void setUp()	This method is used to write resource association code. e.g. Create a database connection.
8.	void tearDown()	This method is used to write resource release code. e.g. Release database connection after performing transaction operation.

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:

S.No.	Method	Description
1.	void addError(Test test, Throwable t)	This method is used if you require add an error to the test.
2.	void addFailure(Test test, AssertionFailedError t)	This method is used if you require add a failure to the list of failures.
3.	void endTest(Test test)	This method is used to notify that a test is performed(completed)
4.	int errorCount()	This method is used to get the error detected during test execution.
5.	Enumeration<TestFailure> errors()	This method simply returns a collection (Enumeration here) of errors.
6.	int failureCount()	This method is used to get the count of errors detected during test execution.
7.	void run(TestCase test)	This method is used to execute a test case.
8.	int runCount()	This method simply counts the executed test.
9.	void startTest(Test test)	This method is used to notify that a test is started.
10.	void stop()	This method is used to test run to be stopped.

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:

S.No.	Method	Description
1.	void addTest(Test test)	This method is used if you want to add a test to the suite.
2.	void addTestSuite(Class<? extends TestCase> testClass)	This method is used if you want to specify the class while adding a test to the suite.
3.	int countTestCases()	This method is used if you want to count the number of test cases.
4.	String getName()	This method is used to get the name of the test suite.
5.	void run(TestResult result)	This method is used to execute a test and collect test result in TestResult object.
6.	void setName(String name)	This method is used to set the name of TestSuite.
7.	Test testAt(int index)	This method is used if you want to return the test at given index.
8.	int testCount()	This method is used if you want to return a number of tests in the Suite.
9.	static Test warning(String message)	This method returns a test which will fail and log a warning message.

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

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What is JUnit Annotations?

JUnit Annotations Example

JunitAnnotationsExample.java

TestRunner.java

Expected Result

Actual Result

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JUnit Assert Class

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Summary