When Tdd Goes Awry

When TDD Goes Awry

Clueless tests, infesting mocks and other horrors...A voyage into today Java

Enterprise worse practices.

Uberto Barbini@ramtop

h0ps://github.com/uberto

Friday, November 1, 13

About me

SHOto start

SHINHeart, mind

In the beginner's mind there are many possibilities, in the expert's mind there are few.

My first program

a·wry (-r)adv.1. In a position that is turned or twisted toward one side; askew.2. Away from the correct course; amiss.

@Test public void testGetSwapType_SPOTFWD() { when(mockTrade.getField(FXSubmitFields.SWAP_TYPE)).thenReturn("SPOTFWD"); setUpTrade("SWAP"); assertEquals(FXSwapType.SPOTFWD, trade.getSwapType());

when(mockTrade.getField(FXSubmitFields.SWAP_TYPE)).thenReturn("SPOTFWD"); setUpTrade("FWDFWDSWAP"); assertEquals(FXSwapType.SPOTFWD, trade.getSwapType()); } private void setUpTrade(final String tradingType) { when(mockTrade.getField(ACCOUNT)).thenReturn(ACCOUNT_VAL); when(mockTrade.getField(CURRENCY_PAIR)).thenReturn(CURRENCY_PAIR_VAL); when(mockTrade.getField(TRADING_TYPE)).thenReturn(tradingType); trade = new FXTrade(mockTrade, USER, mockNearLeg, mockFarLeg); }

Test StoriesEach test should tell a story

Scenario tests illustrate the design

When you are thinking big thoughts, write big tests. When you are thinking little thoughts, write little tests.

Kent Beck, Quora

When you are thinking big thoughts, write big tests. When you are thinking little thoughts, write little tests.

Kent Beck, Quora

Objects are nouns. Good design is a good story. Do you remember XP Metaphor?

My first project

Meaningful test names

Test Driven DesignIt’s a kind of design technique, not a way to test.

When TDD is not useful: when your don’t care about designie. technical spikes, learning exercises

Test Driven DesignIt’s a kind of design technique, not a way to test.

When TDD is not useful: when your don’t care about designie. technical spikes, learning exercises

I get paid for code that works, not for tests, so my philosophy is to test as little as possible to reach a given level of confidence.

Kent Beck Stackoverflow

The caveman house designCarlo Pescio

Question:Why designing for testability result in good design?

The caveman house designCarlo Pescio

Question:Why designing for testability result in good design?

Global stateHidden dependenciesInflexible behavior

Things that work together are kept close

Let’s start from AssertionsOne of the least followed TTD rule says: “There must be one assertion for test”. Why?

The point behind testing one thing at time is the we want to run all the state checks, every time independently.

No IF in the tests.

No logic in the tests, much less duplication with tested logic.

Let’s start from AssertionsOne of the least followed TTD rule says: “There must be one assertion for test”. Why?

The point behind testing one thing at time is the we want to run all the state checks, every time independently.

No IF in the tests.

No logic in the tests, much less duplication with tested logic.

3 typical reasons for many assertions in a test...

Assertion Code

Mocking rulesAt most a single mock and many stubs.

Use stubs for internals and close friends, mocks for collaborators (i.e. listeners)

Stubs can be prepared in setup or with builder helpers. Mocks in the actual test.

Try to verify mocks with actual params or matcher, not any (or maybe you wanted a stub instead?).

Mock-o-meter

0 1 2 3 4 5

Mock-o-meter

0 1 2 3 4 5

If to test 3 lines of simple code, we have 10 lines of complicated test with mocks.

Which is more likely to have a bug? the code or the test?

Mocks Code

High Coupling

In software engineering, coupling or dependency is the degree to which each program module relies on each one of the other modules.antipattern of high coupling:

cohesion refers to the degree to which the elements of a module belong together.[1] Thus, it is a measure of how strongly-related each piece of functionality expressed by the source code of a software module is.

Wikipedia

A little digression: Dependency Injection frameworks

The best classes in any application are the ones that do stuff: the BarcodeDecoder, the KoopaPhysicsEngine, and theAudioStreamer. These classes have dependencies; perhaps a BarcodeCameraFinder, DefaultPhysicsEngine, and anHttpStreamer.

To contrast, the worst classes in any application are the ones that take up space without doing much at all: theBarcodeDecoderFactory, the CameraServiceLoader, and the MutableContextWrapper. These classes are the clumsy duct tape that wires the interesting stuff together.

Dagger is a replacement for these FactoryFactory classes. It allows you to focus on the interesting classes. Declare dependencies, specify how to satisfy them, and ship your app.

from Dagger introductionhttp://square.github.io/dagger/

Good things about Dagger: good and invisible duct tape

Duct Tape is important!

That is, it’s important to wiring up our objects in the best possible way.

Write tests to show how your wiring is done

Replace Duct Tape with Demeter

High Coupling Code

Lasagna Code

Lasagna code, coined in 1982 by Joe Celko, is a type of program structure characterized by several well-defined and separable layers, where each layer of code accesses services in the layers below through well-defined interfaces. [...] A quote usually attributed either to David Wheeler or Butler Lampson reads, "There is no problem in computer science that cannot be solved by adding another layer of indirection, except having too many layers of indirection".

Layer Code

We have a problem,

Our code is too difficult to testWe have a problem,

Our code is too difficult to testLet's write a framework to test it!

We have a problem,

Our code is too difficult to testLet's write a framework to test it!Ok, now we have 2 problems...

We have a problem,

Dedicated test stub must be simple and transparent.They should explain the model, not hide it.

We have a problem,

Same problem for who has to develop against a big framework: even if I have the framework tests, how can I be sure of not losing pieces around? Let's model domain simply as whole and then split it up for the framework.

Dedicated test stub must be simple and transparent.They should explain the model, not hide it.

We have a problem,

How to improve

How to improveIf your tests give you pain don't ignore it. Localize the cause.

Ask to new team members or dev from other teams their impressions.

Experiment and share.

Rule 0: TDD is supposed to be fun and simple.

When Tdd Goes Awry

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