unit testing 101

Unit Testing 101Intro to What, Why, How

Outline

1. What is unit testing?a. what are units?b. testing the future, TDD

2. Why do we unit test? a. advantages

i. refactoringii. maintainability

3. How do we unit test? a. Guidelinesb. Assertionsc. Isolationsd. Mocks vs Stubs

4. Related Stuff

What is Unit Testing?

Kent Beck introduced the term

legacy code: code without tests

What is Unit Testing

Unified Process

Requirements --> Use Cases, Scenarios Scenarios -> Classes, relationships classes(or functions in FP) are the units! Classes -> Unit Tests

Why Unit Testing?

To fail when there is no harm to do sothe cost to fix a bug in different stages

did you think about that in advance?

To refactor code (you can still refactor without UT)

To test after development

Self documenting code (if you read them)

How to do?

● one test, one scenario○ no conditional statements like

■ if, switch etc○ also no loops if possible

■ if there are loops, tests must be broken into other tests

● one test, one assertion● isolated test, not depending on each

○ need dependency, use injection, not arbitrary tests● do not handle exceptions

○ you can assert that an exception will be thrown, though

● tests are not functions of time!

How to do?

when to add tests: ● before new classes/stories● before fixing new bugs

○ preparing the test scenario○ filling the gap

● before introducing new features

you can also write tests for the completed code

How to do

Unit Test Pattern:AAA : Arrange - Act - Assert

An Example in JUnit@RunWith(SpringJUnit4ClassRunner.class)@ContextConfiguration( {"file:test/test-config.xml", "file:web/WEB-INF/application-security.xml", "file:test/test-dao.xml"} )public class MobileUtilsTest {

@Autowired private MobileUtils mobileUtils; @Autowired private BankDao bankDao;

An Example in JUnit

@Test public void testGenerateOtp() throws Exception { Bank bank = bankDao.findByBin("402940"); String otp = mobileUtils.generateOtp(bank); System.out.println(otp); Assert.assertNotNull(otp); }

An Example in JUnit @Test(expected = NullPointerException.class) public void testGenerateNullBankOtp() throws Exception{ try{ Bank bank = null; String otp = mobileUtils.generateOtp(bank); } catch (Exception e){ throw e; } }

How to do

Assertions:● use as many as possible different types of

assertions○ assertThat, assertEquals, assertSame,

assertNotNull○ junit's matchers

● assertion statements must be readable○ self documenting tests○ not assertEquals( result, false )○ please do assertEquals( result, expectedResult )

How to do?

Isolation is important: ● database isolation

○ use a test db if possible● web container isolation

○ use dependency injection if possible■ otherwise it is kind of integration testing

● see spring integration testing

● dependency injection○ provides class isolation

● web services (rest & SOAP)○ use mocks or stubs

● properties (file and system)

How to do?

Automate the tests (otherwise they are meaningless)

use tools like ant, maven

Better use Jenkins!

How to do?

If isolation is important, use mocks and stubs○ mocks

■ use them when you have dependencies that cannot be fulfilled by writing simple stubs● for example, an interface containing many method

declarations○ stubs

■ use them when you call inner methods to test the unit, so you don't have to write inner mocks too

How to do?

Mocks vs Stubs:mocks depend on behavior verificationwhile stubs depend on state verification

examples from Martin Fowler:

Stub examplepublic interface MailService { public void send (Message msg);}public class MailServiceStub implements MailService { private List<Message> messages = new ArrayList<Message>(); public void send (Message msg) {

messages.add(msg); } public int numberSent() {

return messages.size(); }}

Stub Exampleclass OrderStateTester... public void testOrderSendsMailIfUnfilled() {

Order order = new Order(TALISKER, 51);MailServiceStub mailer = new

MailServiceStub();order.setMailer(mailer);order.fill(warehouse);assertEquals(1, mailer.numberSent());

}

Mock Exampleclass OrderInteractionTester... public void testOrderSendsMailIfUnfilled() { Order order = new Order(TALISKER, 51); Mock warehouse = mock(Warehouse.class); Mock mailer = mock(MailService.class); order.setMailer((MailService) mailer.proxy());

mailer.expects(once()).method("send"); warehouse.expects(once()).method("hasInventory") .withAnyArguments() .will(returnValue(false));

order.fill((Warehouse) warehouse.proxy());//verify warehouse.verify(); assertTrue(order.isFilled()); }}

Mocks vs Stubs

it really is a decision for TDDin mocks, you go outside in, one story at a time

usually start from UI

in stubs, you go middle out, also one story, can begin from business objects

if your code is complete, use real objects, whenever possible (better code coverage)

mockists vs classical

a comparison for TDDclassical tries to use the existing objects in

testmockist tries to mock complicated stuff and

dependencies

For Existing Projects

begin add testssubmit to vcskeep tests in a separate folder/moduletest both for success and failuretest the important features first

or just write tests at all end

Relatives, Friends

Code coverageStrive for 100% For starters, each project must have 20%

remember the 20/80 ruleuse tools like http://www.jetbrains.com/idea/features/code_coverage.html

Test Driven Developmentbasis for TDD, write unit tests first!can try if you are starting a new project

Thank you

Questions? (other than why this presentation is in English)