The most important package in JUnit is junit.framework, which contains all the core classes. Some of the important classes are as follows −

Assert Class

Following is the declaration for org.junit.Assert class −

public class Assert extends java.lang.Object

This class provides a set of assertion methods useful for writing tests. Only failed assertions are recorded. Some of the important methods of Assert class are as follows −

Let”s use some of the above-mentioned methods in an example. Create a java class file named TestJunit1.java in C:>JUNIT_WORKSPACE.

import org.junit.Test;
import static org.junit.Assert.*;

public class TestJunit1 {
   @Test
   public void testAdd() {
      //test data
      int num = 5;
      String temp = null;
      String str = "Junit is working fine";

      //check for equality
      assertEquals("Junit is working fine", str);
      
      //check for false condition
      assertFalse(num > 6);

      //check for not null value
      assertNotNull(temp);
   }
}

Next, create a java class file named TestRunner1.java in C:>JUNIT_WORKSPACE to execute test case(s).

import org.junit.runner.JUnitCore;
import org.junit.runner.Result;
import org.junit.runner.notification.Failure;

public class TestRunner1 {
   public static void main(String[] args) {
      Result result = JUnitCore.runClasses(TestJunit1.class);
		
      for (Failure failure : result.getFailures()) {
         System.out.println(failure.toString());
      }
		
      System.out.println(result.wasSuccessful());
   }
}  	

Compile the test case and Test Runner classes using javac.

C:JUNIT_WORKSPACE>javac TestJunit1.java TestRunner1.java

Now run the Test Runner, which will run the test case defined in the provided Test Case class.

C:JUNIT_WORKSPACE>java TestRunner1

Verify the output.

true

TestCase Class

Following is the declaration for org.junit.TestCase class −

public abstract class TestCase extends Assert implements Test

A test case defines the fixture to run multiple tests. Some of the important methods of TestCase class are as follows −

Let”s use some of the above-mentioned methods in an example. Create a java class file named TestJunit2.java in C:>JUNIT_WORKSPACE.

import junit.framework.TestCase;
import org.junit.Before;
import org.junit.Test;

public class TestJunit2 extends TestCase  {
   protected double fValue1;
   protected double fValue2;
   
   @Before 
   public void setUp() {
      fValue1 = 2.0;
      fValue2 = 3.0;
   }
	
   @Test
   public void testAdd() {
      //count the number of test cases
      System.out.println("No of Test Case = "+ this.countTestCases());
		
      //test getName 
      String name = this.getName();
      System.out.println("Test Case Name = "+ name);

      //test setName
      this.setName("testNewAdd");
      String newName = this.getName();
      System.out.println("Updated Test Case Name = "+ newName);
   }
	
   //tearDown used to close the connection or clean up activities
   public void tearDown(  ) {
   }
}

Next, create a java class file named TestRunner2.java in C:>JUNIT_WORKSPACE to execute test case(s).

import org.junit.runner.JUnitCore;
import org.junit.runner.Result;
import org.junit.runner.notification.Failure;

public class TestRunner2 {
   public static void main(String[] args) {
      Result result = JUnitCore.runClasses(TestJunit2.class);
		
      for (Failure failure : result.getFailures()) {
         System.out.println(failure.toString());
      }
		
      System.out.println(result.wasSuccessful());
   }
} 

Compile the test case and Test Runner classes using javac.

C:JUNIT_WORKSPACE>javac TestJunit2.java TestRunner2.java

Now run the Test Runner, which will run the test case defined in the provided Test Case class.

C:JUNIT_WORKSPACE>java TestRunner2

Verify the output.

No of Test Case = 1
Test Case Name = testAdd
Updated Test Case Name = testNewAdd
true

TestResult Class

Following is the declaration for org.junit.TestResult class −

public class TestResult extends Object

A TestResult collects the results of executing a test case. It is an instance of the Collecting Parameter pattern. The test framework distinguishes between failures and errors. A failure is anticipated and checked for with assertions. Errors are unanticipated problems like an ArrayIndexOutOfBoundsException. Some of the important methods of TestResult class are as follows −

Create a java class file named TestJunit3.java in C:>JUNIT_WORKSPACE.

import org.junit.Test;
import junit.framework.AssertionFailedError;
import junit.framework.TestResult;

public class TestJunit3 extends TestResult {
   // add the error
   public synchronized void addError(Test test, Throwable t) {
      super.addError((junit.framework.Test) test, t);
   }

   // add the failure
   public synchronized void addFailure(Test test, AssertionFailedError t) {
      super.addFailure((junit.framework.Test) test, t);
   }
	
   @Test
   public void testAdd() {
      // add any test
   }
   
   // Marks that the test run should stop.
   public synchronized void stop() {
      //stop the test here
   }
}

Next, create a java class file named TestRunner3.java in C:>JUNIT_WORKSPACE to execute test case(s).

import org.junit.runner.JUnitCore;
import org.junit.runner.Result;
import org.junit.runner.notification.Failure;

public class TestRunner3 {
   public static void main(String[] args) {
      Result result = JUnitCore.runClasses(TestJunit3.class);

      for (Failure failure : result.getFailures()) {
         System.out.println(failure.toString());
      }
		
      System.out.println(result.wasSuccessful());
   }
}  	

Compile the test case and Test Runner classes using javac.

C:JUNIT_WORKSPACE>javac TestJunit3.java TestRunner3.java

Now run the Test Runner, which will run the test case defined in the provided Test Case class.

C:JUNIT_WORKSPACE>java TestRunner3

Verify the output.

true

TestSuite Class

Following is the declaration for org.junit.TestSuite class:

public class TestSuite extends Object implements Test

A TestSuite is a Composite of tests. It runs a collection of test cases. Some of the important methods of TestSuite class are as follows −

Create a java class file named JunitTestSuite.java in C:>JUNIT_WORKSPACE to create Test suite.

import junit.framework.*;

public class JunitTestSuite {
   public static void main(String[] a) {
      // add the test''s in the suite
      TestSuite suite = new TestSuite(TestJunit1.class, TestJunit2.class, TestJunit3.class );
      TestResult result = new TestResult();
      suite.run(result);
      System.out.println("Number of test cases = " + result.runCount());
   }
}

Compile the Test suite classes using javac.

C:JUNIT_WORKSPACE>javac JunitTestSuite.java 

Now run the Test Suite.

C:JUNIT_WORKSPACE>java JunitTestSuite

Verify the output.

No of Test Case = 1
Test Case Name = testAdd
Updated Test Case Name = testNewAdd
Number of test cases = 3