Practicing Advanced Unit Testing

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Information about Practicing Advanced Unit Testing

Published on February 15, 2014

Author: BjrnKimminich



Doing Code Katas alone or in a Dojo can help sharpen our elementary skills as software developers. Practicing IDE shortcuts and TDD mini-step cycles is very useful for the daily business, yet I find some existing Code Katas too far away from real-life programming situations. That’s why I came up with the Trading Card Game Kata – which is (very loosely) based on Blizzard Entertainment’s free-to-play online-game “Hearthstone – Heroes of Warcraft”. This Kata is focused on practicing TDD in a slightly more complex (but not complicated) situation where you might have to think about rules like Single Responsibility Principle or Command Query Separation and might even feel the urge to use a Mocking framework at some point.

First I will introduce the ideas of Katas and Dojos in general and explain the TCG Kata rules to you. Then I will demo some real-life best-practices for writing good developer tests, using my TCG Kata sample solution as a showcase. This will include:

* Picking the right Test Double
* Test Data Builders
* Behavior Tests with BDDMockito
* Prose-like Assertions with Hamcrest
* Readability Sugar

The full Kata ruleset and a sample solution in Java 8 can be found on

Practicing Advanced Unit Testing with the «Trading Card Game» Kata Battlecry: Draw a slide. Deathrattle: Transform audience into 1/1 sheep. Speaker v1.11 (05.03.2014)

Kata Kata (型 or 形 literally: "form”) is a Japanese word describing detailed choreographed patterns of movements practiced either solo or in pairs.

Trading Card Game (TCG) A […] trading card game (TCG) […] is a card game that uses specially designed sets of playing cards […] mass-produced for trading or collectibility, and it must have rules for strategic game play. Acquiring these cards may be done by trading with other players or buying card packs.

Why invent another Kata? Bro, why U not use Not TDDfriendly ?? ? ? ? Rules not extensible Too easy

Hearthstone: Heroes of Warcraft®

Kata Trading Card Game

Player Setup Health 30 Mana Hand 0/0 3 4 4 4 5 5 6 6 7 8 Deck 0 0 1 1 2 2 2 3 3 3

Gameplay Receive +1 ReplenishActive Slot Mana Mana Player Pay 1 Mana 0/1 1/1 30 0/0 1 3 5 8 Play Card 1 Draw Card Cause 1 Damage 0/0 29 30 -1 3 2 2

Forced Turn Skip 30 2/2 0/1 1/1 3 5 8 2 29 3 2 2 No affordable Cards 4

Ongoing Gameplay 2/2 30 0/2 1/1 3 5 8 2 4 3 2 2 2 27 29 -2 4

Overload Rule 8/8 18 5 8 6 1 7 2 7/7 Discard Card when Hand already holds 5 Cards 12 0 8 4

Mana Cap 8 10/10 5 6 Mana is capped at 10 Slots 10/10 4 6 1

Bleedout Rule Cause 1 Damage 7 -8 10/10 1 5 6 Drawing from empty Deck 10/10 4 6 1

Game End 7 5 6 10/10 4/10 Winner! 10/10 -6 -2 4 Loser! 6 1

Kata TCG Rules & Variations Detailed rules description Advanced Variations Different cost & damage Healing cards Card drawer cards Use cards as Minions Deck customization

Kata TCG Sample Solution Java 1.8.0 Early Access Lambdas & Stream API Junit 4.11 Mockito 1.9.5 For handling dependencies of tested objects Hamcrest 1.3 Matchers for better readability in assertions System Rules 1.4.0 JUnit @Rules for substituting java.lang.System

Advanced Unit Testing Examples

Skip No-Brainers … Compile Error as Red Test Red Refactor Green

Obvious Implementation Simplest useful step Simplest possible step

Specify the Object under Test Irrelevant Details Implementation Detail Setter introduced for testing Assuming Hidden Default

Define the Object under Test Hidden default problem solved Another unwanted setter

Builder Pattern Prose-like Readability Explicitly listed Expectations …? No unnecessary details

Builder Internals Sensible Default Values Package visible full Constructor needed

Fluent API Setting properties via fluent API

Mocking Behavior Interface has no implementation yet Mock Behavior for this Test

Trashcan Refactoring CardPicker turned out to be overengineered Mocking

Mocking BDD Style Can be confused with Given-When-Then part Can be confused with Given-When-Then part

Mocking BDD Style Sugar coating for BDD syntax Matches its meaning in Given-When-Then structure

Avoid Redundancy Redundant & spoiled with Implementation Details Another slight redundancy

Avoid Constants Disturbs the reading flow

Syntactic Sugar Improves Readability and removes Redundancy

More Syntactic Sugar Magic Numbers Different Level of Abstraction

Syntactic Artificial Sweetener No-Op Syntactic Sugar for Readability Syntactic Sugar reduces Redundancy

Demo | Q&A

Demo: Test Execution Pretty fast All tests pass

Demo: Code Coverage

Demo: Human vs. AI Game Ugly Retro UI Ugly UI Player Input via AI beats me! Again! 

Thank you for your attention!örnKimminich

Credits Background Image: Demonplay (Permission of use granted) Other Images: Blizzard Entertainment (Permission of use requested) Wikipedia, Github, Agile Estonia,,, Hearthstone: Heroes of Warcraft® is a trademark or registered trademark of Blizzard Entertainment, Inc., in the U.S. and/or other countries.

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