Unit testing with JUnit

Unittesting with JUnit

JUnit is a unit testing framework for the Java programming language. JUnit has been important in the development of test-driven development, and is one of a family of unit testing frameworks collectively known as xUnit that originated with JUnit.

Whatis a unit test?

we'll define a unit test as a test of a single isolated component in a repeatable way. Let's go thru that one section at a time to get a clearer idea of what goes into a unit test.

"a test". This means to verify something is correct. In order for us to have a valid unit test, we need to actually validate that after a start condition A, an end condition B exists. "...a single isolated component...". This is what separates a unit test from other types of tests.

 In order for it to be a unit test, it must test something in isolation, aka without dependencies. The reason for this is that we are testing the component itself and not it's interaction with other components (that is an integration test).

Finally, although most definitions don't include this piece, "...in a repeatable way" is a very important piece of the definition. It's one thing to run a test that passes. It's quite different to have something you can run in a repeatable manor at any point to see if changes you made effected how the component behaves. For example, if you choose to do some refactoring to improve performance, can you rerun your unit test to verify that you didn't change the behavior of the component.

Therequirements

In test driven design, we develop the unit test before the functionality. We write a test that verifies that the class should do X after our call. We prove that the test fails, we then create the component to make the test pass. In this case, we are going to create a service with a method that authenticates a user. Below is a class diagram of the scenario.

JUnit class diagram

The interfaces

We will start our coding by defining two interfaces, LoginService and Userx We will implement LoginService, For LoginService, we have a single method that takes a String userName and String password and returns a boolean (true if the user was found, false if it was not). The interface looks like this:

Provides authenticated related processing.

public interface LoginService {

     Handles a request to login.  Passwords are stored as an MD5 Hash in

     this system.  The login service creates a hash based on the paramters

     received and looks up the user.  If a user with the same userName and

     password hash are found, true is returned, else false is returned.

     boolean login(String userName, String password);

}

The Userx  interface will look very similar to the LoginService. It will have a single method that takes a userName and hash. The hash is an MD5 hashed version of the password, provided by the above service.

Provides database access for login related functions

public interface User x{

 Loads a User object for the record that

 is returned with the same username and password.

     User loadByUsernameAndPassword(String userName, String password);

}

The test case

Before we begin development, we will develop our test. Tests are structured by grouping methods that perform a test together in a test case. A test case is a class that extends junit.framework.TestCase. So in this case, we will begin by developing the test case for LoginService. To start, in your test directory, create a new class named LoginServiceTest and make it extend junit.framework.TestCase.

The lifecycle of a test execution consists of three main methods:

public void setUp()

setUp is executed before each of the test. It is used to perform any setup required before the execution of your test. Your implementation will override the default empty implementation in TestCase.

publicvoid testSomething()

testSomething is the actual test method. You may have many of these within a single test case. Each one will be executed by your test runner and all errors will be reported at the end.

public void tearDown()

tearDown is executed after each test method. It is used to perform any cleanup required after your tests.

So to begin flushing out our test case, we'll start with the setUp method. In this method, we'll instantiate an instance of the service to be tested. We'll also create our first mock object, UserDAO. You can see the source of our test below.