Focus on Mock Object(1)

Testing in isolation of Mock Objects: write focused tests that test only a single method, without side effects resulting from other objects relative.

A simple example: Account Manager Problem(based on a Database environment)

Application analysis:

class Account--two attributes: accountId and balance. Three methods: debit(-), credit(+), getBalance--quite simple and not related to other object or enrionment.

class AccountManager--Manage Account, default connect DB to get data from it. Two methods: findAccountForUser and updateAccount. Closely related to object Account and enrionment DataBase.--must be mocked to fit for unit-test.

class AccountService--one attributes: accountManager which you can confige by yourself. Two methods: setAccountManager and transfer.--This is the class we want to test. The transfer method will be testd with class MockAccountManage which implements AccountManager to let the unit-test run easily.

In the real way, solid class which implements AccountManager may connect to a database to gain the data requested. With the MockAccoundManager which tester created to replaced the default behavier of AccounManager, under your control, we can test AccountService singly.

src: http://blog.chinaunix.net/resserver.php?blogId=8755&resource=junit71.txt

import junit.framework.TestCase;

public class TestAccountService extends TestCase {

public void testTransferOK() {

MockAccountManager mockAccountManager = new MockAccountManager();

Account senderAccount = new Account("1", 200);

Account beneficiaryAccount = new Account("2", 100);

mockAccountManager.addAccount("1", senderAccount);

mockAccountManager.addAccount("2", beneficiaryAccount);

AccountService accountService = new AccountService();

accountService.setAccountManager(mockAccountManager);

accountService.transfer("1", "2", 50);

assertEquals(150, senderAccount.getBalance());

assertEquals(150, beneficiaryAccount.getBalance());

}

}