JUnit Framework

JUnit

• JUnit is a unit testing framework for the Java programming language
• JUnit has been important in the development of test-driven development (TDD), and is one of a family of unit testing frameworks(xUnits)
• It is not an automated testing tool, we still have to write our test files by hand
• JUnit does give us some support so that we can write those test files more conveniently

Problems in testing the applications

• In a web application, to test the flow we need to deploy it in the server so if there is a change then again we need to restart the server
• There is no explicit concept of a test passing or failing
• There is no mechanism to collect results in a structured fashion
• More time consuming in Trial and error approach development 

Advantages of JUnit

• Using JUnit we can save testing time
• JUnit tests can be run automatically and they check their own results and provide immediate feedback
• There's no need to manually comb through a report of test results
• No need to build and deploy each time for a minor change
• Using JUnit, If we want to test the application (for web applications) then server is not required so the testing becomes fast 

Members of JUnit

TestSuite

Collection of TestCases, Running a test suite will execute all test classes in that suite in the specified order

TestCase

• A formal written unit test case is characterized by a known input and by an expected output, which is worked out before the test is executed. The known input should test a precondition and the expected output should test a postcondition
• There must be at least two unit test cases for each requirement

Assertion

• These assertion methods typically start with assert and allow you to specify the error message, the expected and the actual result
• An assertion method compares the actual value returned by a test to the expected value, and throws an AssertionException if the comparison test fails

Test Suite Implementations

A test suite class can be implemented in two ways:

• Using TestRunners (org.junit.runner.JUnitCore)
• Using Annotations

TestRunner

public static void main(String[] args) {
Result result = JUnitCore.runClasses(TestClassOne.class,
    TestClassTwo.class);
 }

Annotations

@RunWith(Suite.class)
@Suite.SuiteClasses({ TestClassOne.class,
    TestClassTwo.class})
public class JunitTestSuite {
 }

Test Case Implementations

 A test case class can be implemented in two ways:

• Extending TestCase(junit.framework.TestCase)
• Using Annotations

Extending TestCase

public class DemoTest extends TestCase{
public void test() {
    fail("Failed");
    } 

}

Using Annotations 

@Test
 public void testPrintMessage() {
     System.out.println("Inside testPrintMessage()");
    assertEquals(message, messageUtil.printMessage());
 }

References:

http://java.dzone.com/articles/junit-tutorial-beginners
http://www.vogella.com/tutorials/JUnit/article.html
http://www.tutorialspoint.com/junit/junit_test_framework.htm