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Test Driven Refactoring by Andreas Thies. XP 2004 - Test Driven Refactoring2 Overview Refactoring Bad Smells Unit Tests Unit Tests and Refactoring Special.

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Presentation on theme: "Test Driven Refactoring by Andreas Thies. XP 2004 - Test Driven Refactoring2 Overview Refactoring Bad Smells Unit Tests Unit Tests and Refactoring Special."— Presentation transcript:

1 Test Driven Refactoring by Andreas Thies

2 XP Test Driven Refactoring2 Overview Refactoring Bad Smells Unit Tests Unit Tests and Refactoring Special Smells & Refactorings Review Testing Unit Tests

3 XP Test Driven Refactoring3 Overview Refactoring Bad Smells Unit Tests Unit Tests and Refactoring Special Smells & Refactorings Review Testing Unit Tests

4 XP Test Driven Refactoring4 Whats Refactoring? A change made to the internal structure of software to make it easier to understand to make it cheaper to modify without changing its observable behaviour

5 XP Test Driven Refactoring5 Why should I refactor? Refactoring improves the design of software Refactoring makes software easyer to understand Refactoring helps to find and prevent bugs Refactoring helps you program faster

6 XP Test Driven Refactoring6 When should I refacor Refactor when you need to fix a bug Refactor as you do a code review Refactor when you try to understand other peoples code

7 XP Test Driven Refactoring7 When shouldnt I refactor When starting from the beginning would be easier than refactoring When evaluation is close to a deadline

8 XP Test Driven Refactoring8 Risks (1) Never touch a running system

9 XP Test Driven Refactoring9 Risks (2) Editing code without adding new functionality increases the risk of infiltrating new bugs Refactoring code may remove functionality other developers rely on....

10 XP Test Driven Refactoring10 Risk (3) So what can I to minimize the Risk? Make small steps ! Write extensive test-suites !! Use them after each step !!!

11 XP Test Driven Refactoring11 Catalog of refactorings (1) Add Parameter Change Bidirectional Association to Unidirectional Change Reference to Value Change Unidirectional Association to Bidirectional Change Value to Reference Collapse Hierarchy Consolidate Conditional Expression Consolidate Duplicate Conditional Fragments Convert Dynamic to Static Construction Convert Static to Dynamic Construction Decompose Conditional Duplicate Observed Data Eliminate Inter-Entity Bean Communication Encapsulate Collection Encapsulate Downcast Encapsulate Field Extract Class Extract Interface Extract Method Extract Package Extract Subclass Extract Superclass Form Template Method Hide Delegate Hide Method Hide presentation tier- specific details from the business tier Inline Class Inline Method Inline Temp Introduce A Controller Introduce Assertion Introduce Business Delegate Introduce Explaining Variable Introduce Foreign Method Introduce Local Extension Introduce Null Object Introduce Parameter Object Introduce Synchronizer Token Localize Disparate Logic Merge Session Beans Move Business Logic to Session Move Class Davison Move Field Move Method Parameterize Method Preserve Whole Object Pull Up Constructor Body Pull Up Field Pull Up Method Push Down Field

12 XP Test Driven Refactoring12 Catalog of refactorings (2) Push Down Method Reduce Scope of Variable Refactor Architecture Remove Assignments to Parameters Remove Control Flag Remove Double Negative Remove Middle Man Remove Parameter Remove Setting Method Rename Method Replace Array with Object Replace Assignment with Initialization Replace Conditional with Polymorphism Replace Conditional with Visitor Replace Constructor with Factory Method Replace Data Value with Object Replace Delegation with Inheritance Replace Error Code with Exception Replace Exception with Test Replace Inheritance with Delegation Replace Iteration with Recursion Replace Magic Number with Symbolic Constant Replace Method with Method Object Replace Nested Conditional with Guard Clauses Replace Parameter with Explicit Methods Replace Parameter with Method Replace Record with Data Class Replace Recursion with Iteration Replace Static Variable with Parameter Replace Subclass with Fields Replace Temp with Query Replace Type Code with Class Replace Type Code with State/Strategy Replace Type Code with Subclasses Reverse Conditional Self Encapsulate Field Separate Data Access Code Separate Query from Modifier Split Loop Split Temporary Variable Substitute Algorithm Use a Connection Pool Wrap entities with session

13 XP Test Driven Refactoring13 Overview Refactoring Bad Smells Unit Tests Unit Tests and Refactoring Special Smells & Refactorings Review Testing Unit Tests

14 XP Test Driven Refactoring14 What are Bad Smells anything in your code, where a refactoring seems to be overdue perhaps detectable using certain metrics (?)

15 XP Test Driven Refactoring15 Bad smells (1) Duplicated Code Long Method Large Class Long Parameter List Divergent Change Shotgun Surgery

16 XP Test Driven Refactoring16 Bad smells (2) Switch Statements Lazy Class Speculative Generality Alternative Class with Different Interfaces Data Class Refused Bequest Long comments

17 XP Test Driven Refactoring17 Overview Refactoring Bad Smells Unit Tests Unit Tests and Refactoring Special Smells & Refactorings Review Testing Unit Tests

18 XP Test Driven Refactoring18 Overview Refactoring Bad Smells Unit Tests Unit Tests and Refactoring Special Smells & Refactorings Review Testing Unit Tests

19 XP Test Driven Refactoring19 Validating correctness Because a refactoring dont change the observable behaviour, all unit tests will run afterwards But only, when the refactoring dont manipulate the interface Most refactorings do so!

20 XP Test Driven Refactoring20 Types of refactoring (1) Compatible e.g. split temporary variable no need to update tests Backwards compatible e.g. pull up field add aditional tests

21 XP Test Driven Refactoring21 Types of refactoring (2) Refactorings that can be made backwards compatible e.g. rename method mark the old interface as deprecated add aditional tests Incompatible refactorings e.g. hide method

22 XP Test Driven Refactoring22 Overview Refactoring Bad Smells Unit Tests Unit Tests and Refactoring Special Smells & Refactorings Review Testing Unit Tests

23 XP Test Driven Refactoring23 Bad smells in Unit Test Same as the production code, unit tests are java code also Most of bad smells will fit here too Aditional to this there are few more smells with their own refactorings

24 XP Test Driven Refactoring24 Smell 1: Mystery Guest A test using external recources like a testfile is no longer self contained Introduces hidden depencies This makes it hard to use the test as an aditional documentation

25 XP Test Driven Refactoring25 Mystery Guest: Solution Inline Resource: Set up a fixture in the test code that holds the same contents as the resource

26 XP Test Driven Refactoring26 Smell 2: Recource Optimism Test code make optimistic assumptions about the existence of external resources May introduce non-deterministic behavior

27 XP Test Driven Refactoring27 Recource Optimism: Solution Setup external resources: Make sure the test that uses external resources creates or allocates them before testing.

28 XP Test Driven Refactoring28 Smell 3: Test Run War A test uses special recources making it unable to be run by more than one programmer a time Introduces non-deterministic behaviour

29 XP Test Driven Refactoring29 Test Run War: Solution Make Resources Unique: Use unique identifiers for all resources that are allocated, for example by including a time-stamp

30 XP Test Driven Refactoring30 Smell 4: General Fixture The setUp()-method becomes too general Hard to understand Tests may slow down

31 XP Test Driven Refactoring31 General Fixture: Solution Use Extract Method

32 XP Test Driven Refactoring32 Smell 5: Eager Test One test method checks several methods of the object to be tested Makes test more dependent on each other

33 XP Test Driven Refactoring33 Eger Test: Solution Use Extract Method

34 XP Test Driven Refactoring34 Smell 6: Lazy Test Several test methods check one method of the object to be tested Only all tests execued together have meaning

35 XP Test Driven Refactoring35 Lazy Test: Solution Use Inline Method

36 XP Test Driven Refactoring36 Smell 7: Assertion Roulette Test methods without explanation

37 XP Test Driven Refactoring37 Assertion Roulette: Solution Add Comments !

38 XP Test Driven Refactoring38 Smell 8: Indirect Testing A test class no longer tests only its counterpart in the production code

39 XP Test Driven Refactoring39 Indirect Testing: Solution Problem might be caused in the production code: not enough data hiding! Otherwise: Extract Method / Move Method

40 XP Test Driven Refactoring40 Smell 9: For Testers Only A production class contains methods that are only used by test methods

41 XP Test Driven Refactoring41 For Testers Only: Solution Problem caused in the production code! Remove these methods or if they are needed to set up the tests use Extract Method / Move Method

42 XP Test Driven Refactoring42 Smell 10: Sensitive Equality Comparing by simply using the.toString() method depends on many irrelevant details such as spaces and tabs

43 XP Test Driven Refactoring43 Sensitive Equality: Solution Introduce Equality Method Dont use the.toString() method but introduce a method testing the values itselve.

44 XP Test Driven Refactoring44 Overview Refactoring Bad Smells Unit Tests Unit Tests and Refactoring Special Smells & Refactorings Review Testing Unit Tests

45 XP Test Driven Refactoring45 Bad Smells in Tests – Review Most of bad smells and refactorings will fit for unit tests also There are several special bad smells and refactorings for unit tests Bad smells in unit tests can indicate problems in the production code

46 XP Test Driven Refactoring46 Overview Refactoring Bad Smells Unit Tests Unit Tests and Refactoring Special Smells & Refactorings Review Testing Unit Tests

47 XP Test Driven Refactoring47 Final Question: Can you also test unit tests?

48 XP Test Driven Refactoring48 Code Coverage (1) Report during test which parts of the production code are not executed With this information you can easily find out which parts of the production code are still untested

49 XP Test Driven Refactoring49 Code Coverage (2) CC4J - Code Coverage für Java Applikationen 30 days limited version available gmbh.de/scoop/downloads.htm

50 XP Test Driven Refactoring50 Jester – A JUnit Tester (1) Free available tester for JUnit tests Modifies the production code and reexecutes the tests suites now they should fail, otherwise there are untested functions in production code

51 XP Test Driven Refactoring51 Jester – A JUnit Tester (2) Changes made by Jester: modifying literal numbers changing true to false / false to true changing if( to if(true || changing if( to if(false &&

52 XP Test Driven Refactoring52 Jester – A JUnit Tester (3) Advantages: more powerfull than simple code coverage Disadvantages: very slow – recompiling after each change made needed

53 XP Test Driven Refactoring53 Now: demonstration Jester


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