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An Introduction to Test Driven Development

CodeOps Technologies LLP
CodeOps Technologies LLP

This document provides an overview of test-driven development (TDD). It defines TDD as a technique for building software where tests are written before code to guide development. The key aspects of TDD covered are: - Writing tests first before code, which helps improve design and ensures tests are written. - The TDD mantra of Red-Green-Refactor, where tests initially fail (Red), code is written to pass tests (Green), then code is refactored to improve design. - An example case study of a large Java project developed using TDD that has over 20,000 lines of unit tests providing over 90% test coverage.

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CodeOps Technologies An Overview of Test Driven Development Ganesh Samarthyam ganesh@codeops.tech www.codeops.tech
Old school approach Design Code Test
New school approach Design Test Code
What is TDD? ❖ Test-Driven Development (TDD) is a technique for building software that guides software development by writing tests. (Martin Fowler’s definition) ❖ “Test Driven Development” is NOT primarily about testing or development (i.e., coding) ❖ It is rather about design - where design is evolved through refactoring ❖ Developers write unit tests (NOT testers) and then code
TDD? But I already write unit tests! ❖ In Test Driven Development, tests mean “unit tests” (Note that in variations/extensions such as ATDD, tests are not unit tests) ❖ Just because unit tests are written in a team doesn’t mean they follow TDD - they could be written even after the writing code - that is Plain Old Unit testing (POUting) ❖ However, when following Test Driven Development, or Test First Development approach, we write the tests first before actually writing the code
Writing tests after code: disadvantages ❖ There are many disadvantages in writing tests after code ❖ Testing does not give direct feedback to design and programming => in TDD, the feedback is directly fed back into improving design and programs ❖ Most of the times, after realising the functionality in code, unit testing is omitted => TDD inverts this sequence and helps create unit tests first ❖ Writing tests after developing code often results in “happy path” testing => we don’t have enough granular or “testable” code segments to write the tests
TDD mantra Green Red Refactor failing test(s) passing test(s)
TDD mantra ❖ Red—write a little test that doesn’t work, perhaps doesn’t even compile at first ❖ Green—make the test work quickly, committing whatever sins necessary in the process ❖ Refactor—eliminate all the duplication and smells created in just getting the test to work Source: Test Driven Development: By Example, Kent Beck, 240 pages, Addison-Wesley Professional, 2002;
Make it green, then make it clean! Best Practice
3 laws of TDD ❖ Law 1: You may not write production code unless you’ve first written a failing unit test. ❖ Law 2: You may not write more of a unit test than is sufficient to fail. ❖ Law 3: You may not write more production code than is sufficient to make the failing unit test pass. Source: Professionalism and Test-Driven Development, Robert C. Martin, IEEE Software, 2007
TDD in action: Case study Source: Professionalism and Test-Driven Development, Robert C. Martin, IEEE Software, 2007 ❖ “Over the last few years, Micah Martin and I’ve been working on an application named FitNesse (www.fitnesse.org). ❖ FitNesse is a Web-based application using a Front Controller that defers to servlets that direct views. ❖ Downloaded tens of thousands of times, FitNesse consists of 45,000 lines of Java code in nearly 600 files. ❖ Almost 20,000 of those lines and 200 of those files are unit tests. ❖ Over 1,100 specific test cases contain many thousands of assertions, giving FitNesse test coverage of over 90 percent (as measured by Clover, http://cenqua.com/clover). ❖ These tests execute at the touch of an IDE (integrated development environment) button in approximately 30 seconds. ❖ These tests, along with the convenience of easily executing them, have benefits that far exceed simple software verification.”
TDD process cycle 1. Add a little test 2. Run all tests and fail 3. Make a little change 4. Run the tests and succeed 5. Refactor to remove duplication
TDD and refactoring https://en.wikipedia.org/wiki/Test-driven_development#/media/File:TDD_Global_Lifecycle.png
–Ward Cunningham “You know you are working on clean code when each routine you read turns out to be pretty much what you expected. You can call it beautiful code when the code also makes it look like the language was made for the problem.”
TDD - benefits Better Design Cleaner code (because of refactoring) Safer refactoring Increased quality Better code coverage Tests serve as documentation Faster debugging Most often, the failing code/test is in the most recently changed code Self-documenting tests Test-cases show/indicate how to use the code
Some Java Tools for TDD jWalk Mockito JUnit TestNG
— Esko Luontola “TDD helps with, but does not guarantee, good design & good code. Skill, talent, and expertise remain necessary.”
TDD slows down development?
Unit testing (with JUnit)
Unit testing: common excuses ❖ I am paid to write code, not tests! ❖ I am a developer, not tester - so I’m not responsible for writing tests! ❖ We already have tests - why do we need unit tests? ❖ We are working on a tight deadline - where do I have time for writing unit tests? ❖ I don’t know how to write unit tests ❖ Ours is legacy code - can’t write unit tests for them ❖ If I touch the code, it breaks!
What dependencies can unit test have? ❖ A test is not a unit test if: ❖ It talks to the database ❖ It communicates across the network ❖ It touches the file system ❖ It can’t run at the same time as any of your other unit tests ❖ You have to do special things to your environment (such as editing config files) to run it. — Michael Feathers, in A Set Of Unit Testing Rules (2005)
The law of low-hanging fruit! Start with something really simple. Implement an obvious test case.
F.I.R.S.T Tests ❖ Fast ❖ Independent ❖ Repeatable ❖ Self-validating ❖ Timely
JUnit Original developers Kent Beck, Erich Gamma Stable release JUnit 4.12 GitHub repo https://github.com/junit- team/junit4 License Eclipse Public License (EPL) Website www.junit.org Source: wikipedia
–Martin Fowler (on JUnit) "Never in the field of software engineering has so much been owed by so many to so few lines of code."
Getting started with JUnit ❖ Step 1: Download and Install JUnit ❖ https://github.com/junit-team/junit4/wiki/ Download-and-Install ❖ Step 2: Try “Getting Started” example: ❖ https://github.com/junit-team/junit4/wiki/Getting- started
JUnit ❖ Tests are expressed in ordinary source code ❖ The execution of each test is centered on an instance of a TestCase object ❖ Each TestCase, before it executes the test, has the opportunity to create an environment for the test, and to destroy that environment when the test finishes ❖ Groups of tests can be collected together, and their results of running them all will be reported collectively ❖ We use the language’s exception handling mechanism to catch and report errors Source: Test Driven Development: By Example, Kent Beck, 240 pages, Addison-Wesley Professional, 2002;
Test case structure Setup Execution Validation Cleanup
Assert methods in JUnit assertEquals()/ assertNotEquals() Invokes the equals() methods on the arguments to check whether they are equal assertSame()/ assertNotSame() Uses == on the arguments to check whether they are equal assertTrue()/ assertFalse() Checks if the given boolean argument evaluates to true or false assertNull()/ assertNotNull() Checks if the given argument is null or NOT null assertArrayEquals() Checks if the given array arguments passed have same elements in the same order
Arrange-Act-Assert (AAA) Pattern • Arrange: Setup things needed to execute the tests • Act: Invoke the code under test • Assert: Specify the criteria for the condition to be met for the test to pass (or else, it is test failure) @Test public void evaluatePlus() { // Arrange Expr exprNode = new Plus(new Constant(10), new Constant(20)); // Act int evalValue = exprNode.eval(); // Assert assertEquals(evalValue, 30); }
Test fixtures ❖ You can provide a text fixture to ensure that the test is repeatable, i.e., start in the same state so it produce the same results and clean up after running the tests. ❖ You can use @Before typically to initialise fields. Similarly you can use @After to execute after the test is complete.
Unit testing best practices ❖ Test name should reflect the intent/purpose & describe the feature/specification ❖ Unit test should test a single concept ❖ Readability matters in the tests - use comments as appropriate ❖ Test code also needs maintenance and factors like readability are important (just like production code) ❖ Tests obvious functionality as well as corner cases - both are important
Identify & refactor test smells Best Practice
Duplicate code in unit tests? ❖ Duplicate code segments in code is bad ❖ Violates ‘Don’t Repeat Yourself’ principle ❖ Duplicate code segments in tests is often needed ❖ To test similar but slightly different functionality Isn’t ^C and ^V bad?
Mocking
Tools for mocking EasyMock PowerMock jMock Mockito
Test “doubles” Good tests are Stubs Mocks Fakes
Terminology ❖ System Under Test (SUT) is the part of the system being tested - and could be of different levels of granularity like a class or an application. ❖ Depended On Component (DOC) means the entity that SUT requires to fulfil its objectives. ❖ Mocking can be used to decouple SUT from DOCs - this enables unit tests to run independently
Test “doubles” ❖ Simplest one is stub ❖ It is a temporary one that does nothing and stands for the real object ❖ More sophisticated than stub is a fake ❖ It provides an alternative simple implementation than the original one ❖ Mocks simulate the original object ❖ Provides implementation of the object with assertions, returning hard-coded values, etc
“Fake it till you make it” TDD Principle
Fakes ❖ Fake is a type of test double. ❖ It is simpler, easier, or cheaper to use than the actual dependency. ❖ An example is using “HSQLDB” (in-memory database) instead of actual “Microsoft SQL” database. ❖ Fakes are mainly used in integration tests.
Why “test doubles”? ❖ Allow us to implement the code for specific functionality without getting all the dependent code in place (without getting “dragged down” by dependencies) ❖ Can independently test only the given functionality ❖ If it fails, we know its because of the given code and not due to dependencies
Stub-outs ❖ Plumbing - “Stub-Outs” - Short pipes put in early during plumbing work during constructions - eventually, they will be replaced with real pipes and fixtures.
Related topics
Preparatory refactoring Source: https://martinfowler.com/articles/preparatory-refactoring-example.html
Acceptance TDD Story Automate tests Write testsImplement feature
Code quality tools CheckStyle IntelliJ IDEA/ Eclipse analysers PMD FindBugs
Image credits ❖ https://s-media-cache-ak0.pinimg.com/736x/78/c9/9e/78c99e530a69406ec249588ef87a59a9.jpg ❖ http://www.datamation.com/imagesvr_ce/4130/development-driven.jpg ❖ https://s-media-cache-ak0.pinimg.com/736x/ae/22/01/ae2201013b69918a20b6de0adf1517a1.jpg ❖ http://blog.itexus.com/img/tdd_comics.png ❖ https://martinfowler.com/articles/preparatory-refactoring-example/jessitron.png ❖ https://i2.wp.com/www.gilzilberfeld.com/wp-content/uploads/2011/02/regret-testing.png ❖ https://pixabay.com/en/pegasus-horse-winged-mythology-586124/ ❖ https://pixabay.com/en/horse-gallop-horses-standard-1401914/ ❖ https://refactoring.guru/images/content-public/index-clean-code.png ❖ http://www.lifeisanecho.com/wp-content/uploads/2016/06/ar131070344825846.jpg ❖ https://pixabay.com/en/ball-chain-bug-jail-insect-46207/ ❖ https://pixabay.com/en/home-old-school-old-old-building-1824815/ ❖ https://pixabay.com/en/escalator-stairs-metal-segments-283448/ ❖ https://devops.com/wp-content/uploads/2016/07/tdd-01-1.jpg ❖ http://www.nanrussell.com/wp-content/uploads/2015/08/Not-me.jpg ❖ https://cdn.meme.am/instances/500x/43446748/winter-is-coming-brace-yourselves-endless-client-revisions-are-coming.jpg ❖ https://t4.ftcdn.net/jpg/00/87/17/55/240_F_87175567_I7FK0h2XNxrwtnoYbufTzvpLv3p2cFrk.jpg ❖ https://cdn.meme.am/cache/instances/folder518/500x/64808518/yeah-if-you-could-just-if-we-could-stop-changing-requirements-every-5-minutes-that-would-be-great.jpg
Image credits ❖ http://optymyze.com/blog/wp-content/uploads/sites/2/2017/02/change.jpg ❖ http://bookboon.com/blog/wp-content/uploads/2014/03/D%C3%A9veloppez-votre-potentiel.jpg ❖ https://techbeacon.com/sites/default/files/most_interesting_man_test_in_production_meme.jpg ❖ https://cdn-images-1.medium.com/max/490/1*k-OkcZd2fAyZf1WBkharGA.jpeg ❖ https://akchrish23.files.wordpress.com/2012/12/far-side-first-pants-then-your-shoes.jpg ❖ https://image.slidesharecdn.com/its-all-about-design-1232847245981881-1/95/its-all-about-design-10-728.jpg?cb=1232825731 ❖ http://www.fox1023.com/wp-content/uploads/2016/06/fail-sign1.jpg ❖ https://vgarmada.files.wordpress.com/2012/04/pass-sign.jpg ❖ http://codelikethis.com/lessons/agile_development/make-it-green.png ❖ https://refactoring.guru/images/content-public/index-refactoring-how.png ❖ http://geek-and-poke.com/geekandpoke/2014/1/15/philosophising-geeks ❖ https://employmentdiscrimination.foxrothschild.com/wp-content/uploads/sites/18/2014/06/20350757_s.jpg ❖ https://static1.squarespace.com/static/5783a7e19de4bb11478ae2d8/t/5821d2ea09e1c46748737af1/1478614300894/shutterstock_217082875-e1459952801830.jpg ❖ https://lh3.googleusercontent.com/-eM1_28qE1cM/U1bUFmBU1NI/AAAAAAAAHEk/ZqLcxFEhMuA/w530-h398-p/slide-32-638.jpg ❖ http://www.trainingforwarriors.com/wp-content/uploads/2015/03/3-Laws-Post.jpg
Image credits ❖ https://patientsrising.org/sites/default/files/Step%20Therapy.PNG ❖ https://1.bp.blogspot.com/-Q00OoZelCic/WFSmGIUCrGI/AAAAAAAAx5U/i59y1h- czIIXNswq6aMdAOUGjgPLaPdxACLcB/s1600/awful.png ❖ http://s2.quickmeme.com/img/f4/f4b4744206cf737305f1a4619fefde7b0df54ecc0dc012adcceaadf93196a7e8.jpg ❖ https://pbs.twimg.com/media/CeZu1YjUsAEfhcP.jpg:large ❖ https://upload.wikimedia.org/wikipedia/en/thumb/f/ff/Poison_Help.svg/1024px-Poison_Help.svg.png ❖ http://data.whicdn.com/images/207820816/large.jpg ❖ http://orig04.deviantart.net/c7cb/f/2014/171/d/a/the_bare_minimum_bandits_by_shy_waifu-d7n8813.png ❖ http://fistfuloftalent.com/wp-content/uploads/2017/04/3c0f8f4.jpg
References ❖ Wikipedia page - JUnit: https://en.wikipedia.org/ wiki/JUnit ❖ Wikipedia page - Test Driven Development: https:// en.wikipedia.org/wiki/Test-driven_development ❖ Professionalism and TDD: https://8thlight.com/blog/ uncle-bob/2014/05/02/ProfessionalismAndTDD.html ❖ Preparatory refactoring: https://martinfowler.com/ articles/preparatory-refactoring-example.html
Recommended reading Test Driven Development: By Example, Kent Beck, 240 pages, Addison-Wesley Professional, 2002; Classic on TDD by its originator Kent Beck
Recommended reading Covers principles, best practices, heuristics, and interesting examples Growing Object-Oriented Software, Guided by Tests, Steve Freeman, Nat Pryce, Addison Wesley, 2009
Recommended reading Covers design smells as violations of design principles “Refactoring for Software Design Smells: Managing Technical Debt”, Girish Suryanarayana, Ganesh Samarthyam, Tushar Sharma, ISBN - 978-0128013977, Morgan Kaufmann/Elsevier, 2014.
ganesh@codeops.tech @GSamarthyam www.codeops.tech slideshare.net/sgganesh +91 98801 64463 bit.ly/sgganesh

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An Introduction to Test Driven Development

  • 1. CodeOps Technologies An Overview of Test Driven Development Ganesh Samarthyam [email protected] www.codeops.tech
  • 4. What is TDD? ❖ Test-Driven Development (TDD) is a technique for building software that guides software development by writing tests. (Martin Fowler’s definition) ❖ “Test Driven Development” is NOT primarily about testing or development (i.e., coding) ❖ It is rather about design - where design is evolved through refactoring ❖ Developers write unit tests (NOT testers) and then code
  • 5. TDD? But I already write unit tests! ❖ In Test Driven Development, tests mean “unit tests” (Note that in variations/extensions such as ATDD, tests are not unit tests) ❖ Just because unit tests are written in a team doesn’t mean they follow TDD - they could be written even after the writing code - that is Plain Old Unit testing (POUting) ❖ However, when following Test Driven Development, or Test First Development approach, we write the tests first before actually writing the code
  • 6. Writing tests after code: disadvantages ❖ There are many disadvantages in writing tests after code ❖ Testing does not give direct feedback to design and programming => in TDD, the feedback is directly fed back into improving design and programs ❖ Most of the times, after realising the functionality in code, unit testing is omitted => TDD inverts this sequence and helps create unit tests first ❖ Writing tests after developing code often results in “happy path” testing => we don’t have enough granular or “testable” code segments to write the tests
  • 8. TDD mantra ❖ Red—write a little test that doesn’t work, perhaps doesn’t even compile at first ❖ Green—make the test work quickly, committing whatever sins necessary in the process ❖ Refactor—eliminate all the duplication and smells created in just getting the test to work Source: Test Driven Development: By Example, Kent Beck, 240 pages, Addison-Wesley Professional, 2002;
  • 9. Make it green, then make it clean! Best Practice
  • 10. 3 laws of TDD ❖ Law 1: You may not write production code unless you’ve first written a failing unit test. ❖ Law 2: You may not write more of a unit test than is sufficient to fail. ❖ Law 3: You may not write more production code than is sufficient to make the failing unit test pass. Source: Professionalism and Test-Driven Development, Robert C. Martin, IEEE Software, 2007
  • 11. TDD in action: Case study Source: Professionalism and Test-Driven Development, Robert C. Martin, IEEE Software, 2007 ❖ “Over the last few years, Micah Martin and I’ve been working on an application named FitNesse (www.fitnesse.org). ❖ FitNesse is a Web-based application using a Front Controller that defers to servlets that direct views. ❖ Downloaded tens of thousands of times, FitNesse consists of 45,000 lines of Java code in nearly 600 files. ❖ Almost 20,000 of those lines and 200 of those files are unit tests. ❖ Over 1,100 specific test cases contain many thousands of assertions, giving FitNesse test coverage of over 90 percent (as measured by Clover, http://cenqua.com/clover). ❖ These tests execute at the touch of an IDE (integrated development environment) button in approximately 30 seconds. ❖ These tests, along with the convenience of easily executing them, have benefits that far exceed simple software verification.”
  • 12. TDD process cycle 1. Add a little test 2. Run all tests and fail 3. Make a little change 4. Run the tests and succeed 5. Refactor to remove duplication
  • 14. –Ward Cunningham “You know you are working on clean code when each routine you read turns out to be pretty much what you expected. You can call it beautiful code when the code also makes it look like the language was made for the problem.”
  • 15. TDD - benefits Better Design Cleaner code (because of refactoring) Safer refactoring Increased quality Better code coverage Tests serve as documentation Faster debugging Most often, the failing code/test is in the most recently changed code Self-documenting tests Test-cases show/indicate how to use the code
  • 16. Some Java Tools for TDD jWalk Mockito JUnit TestNG
  • 17. — Esko Luontola “TDD helps with, but does not guarantee, good design & good code. Skill, talent, and expertise remain necessary.”
  • 18. TDD slows down development?
  • 20. Unit testing: common excuses ❖ I am paid to write code, not tests! ❖ I am a developer, not tester - so I’m not responsible for writing tests! ❖ We already have tests - why do we need unit tests? ❖ We are working on a tight deadline - where do I have time for writing unit tests? ❖ I don’t know how to write unit tests ❖ Ours is legacy code - can’t write unit tests for them ❖ If I touch the code, it breaks!
  • 21. What dependencies can unit test have? ❖ A test is not a unit test if: ❖ It talks to the database ❖ It communicates across the network ❖ It touches the file system ❖ It can’t run at the same time as any of your other unit tests ❖ You have to do special things to your environment (such as editing config files) to run it. — Michael Feathers, in A Set Of Unit Testing Rules (2005)
  • 22. The law of low-hanging fruit! Start with something really simple. Implement an obvious test case.
  • 23. F.I.R.S.T Tests ❖ Fast ❖ Independent ❖ Repeatable ❖ Self-validating ❖ Timely
  • 24. JUnit Original developers Kent Beck, Erich Gamma Stable release JUnit 4.12 GitHub repo https://github.com/junit- team/junit4 License Eclipse Public License (EPL) Website www.junit.org Source: wikipedia
  • 25. –Martin Fowler (on JUnit) "Never in the field of software engineering has so much been owed by so many to so few lines of code."
  • 26. Getting started with JUnit ❖ Step 1: Download and Install JUnit ❖ https://github.com/junit-team/junit4/wiki/ Download-and-Install ❖ Step 2: Try “Getting Started” example: ❖ https://github.com/junit-team/junit4/wiki/Getting- started
  • 27. JUnit ❖ Tests are expressed in ordinary source code ❖ The execution of each test is centered on an instance of a TestCase object ❖ Each TestCase, before it executes the test, has the opportunity to create an environment for the test, and to destroy that environment when the test finishes ❖ Groups of tests can be collected together, and their results of running them all will be reported collectively ❖ We use the language’s exception handling mechanism to catch and report errors Source: Test Driven Development: By Example, Kent Beck, 240 pages, Addison-Wesley Professional, 2002;
  • 29. Assert methods in JUnit assertEquals()/ assertNotEquals() Invokes the equals() methods on the arguments to check whether they are equal assertSame()/ assertNotSame() Uses == on the arguments to check whether they are equal assertTrue()/ assertFalse() Checks if the given boolean argument evaluates to true or false assertNull()/ assertNotNull() Checks if the given argument is null or NOT null assertArrayEquals() Checks if the given array arguments passed have same elements in the same order
  • 30. Arrange-Act-Assert (AAA) Pattern • Arrange: Setup things needed to execute the tests • Act: Invoke the code under test • Assert: Specify the criteria for the condition to be met for the test to pass (or else, it is test failure) @Test public void evaluatePlus() { // Arrange Expr exprNode = new Plus(new Constant(10), new Constant(20)); // Act int evalValue = exprNode.eval(); // Assert assertEquals(evalValue, 30); }
  • 31. Test fixtures ❖ You can provide a text fixture to ensure that the test is repeatable, i.e., start in the same state so it produce the same results and clean up after running the tests. ❖ You can use @Before typically to initialise fields. Similarly you can use @After to execute after the test is complete.
  • 32. Unit testing best practices ❖ Test name should reflect the intent/purpose & describe the feature/specification ❖ Unit test should test a single concept ❖ Readability matters in the tests - use comments as appropriate ❖ Test code also needs maintenance and factors like readability are important (just like production code) ❖ Tests obvious functionality as well as corner cases - both are important
  • 33. Identify & refactor test smells Best Practice
  • 34. Duplicate code in unit tests? ❖ Duplicate code segments in code is bad ❖ Violates ‘Don’t Repeat Yourself’ principle ❖ Duplicate code segments in tests is often needed ❖ To test similar but slightly different functionality Isn’t ^C and ^V bad?
  • 36. Tools for mocking EasyMock PowerMock jMock Mockito
  • 37. Test “doubles” Good tests are Stubs Mocks Fakes
  • 38. Terminology ❖ System Under Test (SUT) is the part of the system being tested - and could be of different levels of granularity like a class or an application. ❖ Depended On Component (DOC) means the entity that SUT requires to fulfil its objectives. ❖ Mocking can be used to decouple SUT from DOCs - this enables unit tests to run independently
  • 39. Test “doubles” ❖ Simplest one is stub ❖ It is a temporary one that does nothing and stands for the real object ❖ More sophisticated than stub is a fake ❖ It provides an alternative simple implementation than the original one ❖ Mocks simulate the original object ❖ Provides implementation of the object with assertions, returning hard-coded values, etc
  • 40. “Fake it till you make it” TDD Principle
  • 41. Fakes ❖ Fake is a type of test double. ❖ It is simpler, easier, or cheaper to use than the actual dependency. ❖ An example is using “HSQLDB” (in-memory database) instead of actual “Microsoft SQL” database. ❖ Fakes are mainly used in integration tests.
  • 42. Why “test doubles”? ❖ Allow us to implement the code for specific functionality without getting all the dependent code in place (without getting “dragged down” by dependencies) ❖ Can independently test only the given functionality ❖ If it fails, we know its because of the given code and not due to dependencies
  • 43. Stub-outs ❖ Plumbing - “Stub-Outs” - Short pipes put in early during plumbing work during constructions - eventually, they will be replaced with real pipes and fixtures.
  • 47. Code quality tools CheckStyle IntelliJ IDEA/ Eclipse analysers PMD FindBugs
  • 48. Image credits ❖ https://s-media-cache-ak0.pinimg.com/736x/78/c9/9e/78c99e530a69406ec249588ef87a59a9.jpg ❖ http://www.datamation.com/imagesvr_ce/4130/development-driven.jpg ❖ https://s-media-cache-ak0.pinimg.com/736x/ae/22/01/ae2201013b69918a20b6de0adf1517a1.jpg ❖ http://blog.itexus.com/img/tdd_comics.png ❖ https://martinfowler.com/articles/preparatory-refactoring-example/jessitron.png ❖ https://i2.wp.com/www.gilzilberfeld.com/wp-content/uploads/2011/02/regret-testing.png ❖ https://pixabay.com/en/pegasus-horse-winged-mythology-586124/ ❖ https://pixabay.com/en/horse-gallop-horses-standard-1401914/ ❖ https://refactoring.guru/images/content-public/index-clean-code.png ❖ http://www.lifeisanecho.com/wp-content/uploads/2016/06/ar131070344825846.jpg ❖ https://pixabay.com/en/ball-chain-bug-jail-insect-46207/ ❖ https://pixabay.com/en/home-old-school-old-old-building-1824815/ ❖ https://pixabay.com/en/escalator-stairs-metal-segments-283448/ ❖ https://devops.com/wp-content/uploads/2016/07/tdd-01-1.jpg ❖ http://www.nanrussell.com/wp-content/uploads/2015/08/Not-me.jpg ❖ https://cdn.meme.am/instances/500x/43446748/winter-is-coming-brace-yourselves-endless-client-revisions-are-coming.jpg ❖ https://t4.ftcdn.net/jpg/00/87/17/55/240_F_87175567_I7FK0h2XNxrwtnoYbufTzvpLv3p2cFrk.jpg ❖ https://cdn.meme.am/cache/instances/folder518/500x/64808518/yeah-if-you-could-just-if-we-could-stop-changing-requirements-every-5-minutes-that-would-be-great.jpg
  • 49. Image credits ❖ http://optymyze.com/blog/wp-content/uploads/sites/2/2017/02/change.jpg ❖ http://bookboon.com/blog/wp-content/uploads/2014/03/D%C3%A9veloppez-votre-potentiel.jpg ❖ https://techbeacon.com/sites/default/files/most_interesting_man_test_in_production_meme.jpg ❖ https://cdn-images-1.medium.com/max/490/1*k-OkcZd2fAyZf1WBkharGA.jpeg ❖ https://akchrish23.files.wordpress.com/2012/12/far-side-first-pants-then-your-shoes.jpg ❖ https://image.slidesharecdn.com/its-all-about-design-1232847245981881-1/95/its-all-about-design-10-728.jpg?cb=1232825731 ❖ http://www.fox1023.com/wp-content/uploads/2016/06/fail-sign1.jpg ❖ https://vgarmada.files.wordpress.com/2012/04/pass-sign.jpg ❖ http://codelikethis.com/lessons/agile_development/make-it-green.png ❖ https://refactoring.guru/images/content-public/index-refactoring-how.png ❖ http://geek-and-poke.com/geekandpoke/2014/1/15/philosophising-geeks ❖ https://employmentdiscrimination.foxrothschild.com/wp-content/uploads/sites/18/2014/06/20350757_s.jpg ❖ https://static1.squarespace.com/static/5783a7e19de4bb11478ae2d8/t/5821d2ea09e1c46748737af1/1478614300894/shutterstock_217082875-e1459952801830.jpg ❖ https://lh3.googleusercontent.com/-eM1_28qE1cM/U1bUFmBU1NI/AAAAAAAAHEk/ZqLcxFEhMuA/w530-h398-p/slide-32-638.jpg ❖ http://www.trainingforwarriors.com/wp-content/uploads/2015/03/3-Laws-Post.jpg
  • 50. Image credits ❖ https://patientsrising.org/sites/default/files/Step%20Therapy.PNG ❖ https://1.bp.blogspot.com/-Q00OoZelCic/WFSmGIUCrGI/AAAAAAAAx5U/i59y1h- czIIXNswq6aMdAOUGjgPLaPdxACLcB/s1600/awful.png ❖ http://s2.quickmeme.com/img/f4/f4b4744206cf737305f1a4619fefde7b0df54ecc0dc012adcceaadf93196a7e8.jpg ❖ https://pbs.twimg.com/media/CeZu1YjUsAEfhcP.jpg:large ❖ https://upload.wikimedia.org/wikipedia/en/thumb/f/ff/Poison_Help.svg/1024px-Poison_Help.svg.png ❖ http://data.whicdn.com/images/207820816/large.jpg ❖ http://orig04.deviantart.net/c7cb/f/2014/171/d/a/the_bare_minimum_bandits_by_shy_waifu-d7n8813.png ❖ http://fistfuloftalent.com/wp-content/uploads/2017/04/3c0f8f4.jpg
  • 51. References ❖ Wikipedia page - JUnit: https://en.wikipedia.org/ wiki/JUnit ❖ Wikipedia page - Test Driven Development: https:// en.wikipedia.org/wiki/Test-driven_development ❖ Professionalism and TDD: https://8thlight.com/blog/ uncle-bob/2014/05/02/ProfessionalismAndTDD.html ❖ Preparatory refactoring: https://martinfowler.com/ articles/preparatory-refactoring-example.html
  • 52. Recommended reading Test Driven Development: By Example, Kent Beck, 240 pages, Addison-Wesley Professional, 2002; Classic on TDD by its originator Kent Beck
  • 53. Recommended reading Covers principles, best practices, heuristics, and interesting examples Growing Object-Oriented Software, Guided by Tests, Steve Freeman, Nat Pryce, Addison Wesley, 2009
  • 54. Recommended reading Covers design smells as violations of design principles “Refactoring for Software Design Smells: Managing Technical Debt”, Girish Suryanarayana, Ganesh Samarthyam, Tushar Sharma, ISBN - 978-0128013977, Morgan Kaufmann/Elsevier, 2014.