learn test driven development in java

Test Driven Developmentin Java

Wednesday, 14 November 12

About me!

Matthew Todd matthew.todd@fluentsoftware.co.uk

@matthew_todd

Working with developers, continuously improving agile practice

What is TDD?

Testing timeline

1989: First tests on punchcards

1994: Kent Beck creates SUnit test framework

1995: TDD Demo

1999: Extreme programming explained published

2000: JUnit.org launched

Manifesto for Agile Software DevelopmentWe are uncovering better ways of developingsoftware by doing it and helping others do it.Through this work we have come to value:

Individuals and interactions over processes and tools

Working software over comprehensive documentationCustomer collaboration over contract negotiation

Responding to change over following a planThat is, while there is value in the items on

the right, we value the items on the left more

Test spectrum

Single function test

Full system test

Automated integration/acceptance

Unit test

Testing in concert

Component test

1. Write test

2. Test fails!

1. Write test

2. Test fails!

1. Write test

3. Write code

2. Test fails!

1. Write test

3. Write code

4. Test passes!

2. Test fails!

1. Write test

3. Write code

4. Test passes!

5. Refactor

2. Test fails!

1. Write test

3. Write code

4. Test passes!

5. Refactor

Why TDD?

Proactive VS Reactive

Seek out problems early on

Validate requirements

Validate code

Test late

Only respond to defects

Focused on debugging

Unit test Live system

Relative cost of change

RequirementsDrive out requirements issues early

Rapid feedbackMany small changes VS One Big Change™

CollaborationEnables developers to work together

Values refactoringRefactor often to lower impact and risk

Design to testTesting driving good design practice

Tests as informationDocumenting decisions and assumptions

Sounds great!So show me

So, let’s get started

Reverse polish calculator3 4 +

Calculator walkthrough

Reverse polish calculatorDeveloped using a test driven approach

“sounds simple, but what about real applications?”

Single responsibilityOLID

SOpen/ClosedLID

SOLiskov SubstitutionID

SOLInterface segregationD

SOLIDependency inversion

Isolating dependencies

Test target

Dependency

Test double

Test DoublesFakes MocksStubs

Providing state-based verificationStubs

FakesProviding simplified replacements

MocksProviding behaviour based verification

Stubs Assertions made directly in test methodFakes

Mocks Assertions made by mock object

Test double demonstration

Mock frameworks

Test balanceConsider mock frameworks where appropriate

Dealing with the legacy

Dealing with the legacySomeone else’s code? No interfaces?

Code we cannot change

So, now we can test it!

So, now we can test it!What makes a good test?

Test principles

FastIRST

FIndependentRST

FIRepeatableST

FIRSelf-validatingT

FIRSTimely

TDD Anti-patterns

Anti-pattern: the singleton

Who uses this singleton?

Who owns this singleton?

What behaviours does it provide?

Anti-pattern: create the world

@Before public void initialiseTests() { loadBalancer = createMockLoadBalancingService(); server1 = createMockServer(); server2 = createMockServer(); loadBalancer.addServer(server1); loadBalancer.addServer(server2); dbEngine = new DBEngine(); dbEngine.addTable("users"); dbEngine.addTable("profiles"); dbEngine.addTable("posts"); userProfileService = new Mock<UserProfileServer>(); adminUser = new User("admin",true); user1 = new User("alice",false); user2 = new User("bob",false); userProfileService.register(user1); userProfileService.register(user2); user1.connectWith(user2); ...

Anti-pattern: create the world

Test burden increases over time

Test complexity increases

Often a sign of application complexity

Anti-pattern: completely mocked

@Test public void testingNothing() { MockServiceFactory factory = new MockServiceFactory(); Mock<UserService> userService = new Mock<UserService>(); factory.add(userService); User user = new User("bob"); userService.add(user); assertEquals("bob",userService.getUsers()[0].name()); }

Test boundariesClass(es) under test Out of test scope

Anti-pattern: exceptional test

@Test public void testUserCreation() { userService.createUser("bob"); }

Anti-pattern: exceptional test

Good coverage, but poor validation

@Test public void testUserCreation() { userService.createUser("bob"); }

Anti-pattern: usually passes

com.example.UncertainTest

Anti-pattern: usually passes

We need to be able to trust our tests

Control threading and access to resources

Anti-pattern: one big test

@Test public void testEverything() { userService.createUser("alice"); assertEquals(1,userService.getUserCount()); userService.createUser("alice"); assertEquals(1,userService.getUserCount()); userService.createUser("bob"); assertEquals(2,userService.getUserCount()); userService.dropUser("alice"); assertEquals(1,userService.getUserCount()); User bob = userService.getUser("bob"); assertNotNull(bob); ...

Anti-pattern: one big test

testEverything

testUserCreation

testCreatingDuplicateUser

testDroppingUser

Anti-pattern: the slow test

Should be quick to pass

Should be quick to fail

Run frequently

Anti-pattern: second-class test

@Test public void whoKnowsWhatThisTests() { createTestObjects(); testUser.setName("alice"); setupTestDependencies(); User user2 = new User("user2"); setupUser(user2); testManager.add(testUser); ... test(user2); }

Applying TDD

When not to use TDD!

BDDIntegration testing

Design

Continuous delivery

Manual testing

User stories

Practice practice practice

TDD Kata

TDD Kata roman numerals1 - convert text from normal numerals ->

Roman numerals

2 - convert in the other direction too

TDD Kata FizzBuzz

printing numbers from 1 to 100

..but multiples of 3 should print Fizzmultiples of 5 should print Buzzmultiples of 3 and 5 print FizzBuzz

1 2 Fizz 4 Buzz Fizz 7 ...

TDD Kata roman calculatorcalculator only accepting roman numerals as

input and output

I + III = IV

TDD Kata tennisimplement simple tennis game

http://en.wikipedia.org/wiki/Tennis#Scoring

Thank you!

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