Hi Sargun, first we need to create a test class with a test method annotated with @Test as given below:
FirstClassTest.java
package testingDemo.JUnit;  
import static org.JUnit.Assert.*;
import org.JUnit.Test;
public class FirstClassTest {
    @Test
    public void FirstMethod(){
        String str= "JUnit is working fine";
        assertEquals("JUnit is working fine",str);
    }
}
To execute our above test method ,we need to create a test runner. In the test runner we have to add test class as a parameter in JUnitCore's runclasses() method . It will return the test result, based on whether the test is passed or failed:
package testingDemo.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(MyFirstClassTest.class);					
			for (Failure failure : result.getFailures()) {							
              System.out.println(failure.toString());					
      }		
      System.out.println("Result=="+result.wasSuccessful());							
   }		
}