TTD Test-Driven Development � Create a formal, executable specification of what to do � �
What is it � TDD is a software development approach whereby you write your test cases before you write any program text � � TDD–2
What is it – 2 � TDD is a software development approach whereby you write your test cases before you write any implementation program text � You will already have defined the requirement for the class, an initial specification for the class, and an initial design for the class � � TDD–3
What is it – 3 � TDD is a software development approach whereby you write your test cases before you write any implementation program text � You will already have defined the requirement for the class, an initial specification for the class, and an initial design for the class � Tests drive or dictate the order in which the program text is developed � � TDD–4
What is it – 4 � TDD is a software development approach whereby you write your test cases before you write any implementation program text � You will already have defined the requirement for the class, an initial specification for the class, and an initial design for the class � Test cases dictate the order in which the program text is developed � By the order in which tests are satisfied � � TDD–5
What is it – 5 � TDD is a software development approach whereby you write your test cases before you write any implementation program text � You will already have defined the requirement for the class, an initial specification for the class, and an initial design for the class � Test cases dictate the order in which the program text is developed � By the order in which tests are satisfied � The intent of the test cases is to � Provide a formal, executable specification of what a the unit is to do � As a consequence, Some test cases are � A part of the specification document for independent features � A part of the design document to verify consistent and proper implementation � � TDD–6
TDD stages � Write a single test � Compile it – compilation will fail, as you have no implementation � Implement just enough program text to get the test to compile � Run the test – see it fail � Implement just enough program text to get the test to pass � Run the test and it pass � Refactor � Repeat � TDD–7
TDD stages � Write a test Refactor & Compile test Run test Fix compile Watch it pass errors Run program test Run test Watch it pass Watch it fail TDD–8
How does this affect you? � Before you write program text, think about what it will do � TDD–9
How does this affect you? – 2 � Before you write program text, think about what it will do � Write the test cases that use methods that are not even implemented yet � TDD–10
How does this affect you? – 3 � Before you write program text, think about what it will do � Write the test cases that use methods that are not even implemented yet � A test is not something you do it is something you write and run once, twice, three times, etc. etc. etc. � TDD–11
How does this affect you? – � Before you write program text, think about what it will do � Write the test cases that use methods that are not even implemented yet � A test is not something you do it is something you write and run once, twice, three times, etc. etc. etc. � It is program text – a formal, executable specification � You have test automation so you can repeatedly test your system even after small changes (regression testing) � TDD–12
How does this affect you? – 5 � Before you write program text, think about what it will do � Write the test cases that use methods that are not even implemented yet � A test is not something you do it is something you write and run once, twice, three times, etc. etc. etc. � It is program text – a formal, executable specification � You have test automation so you can repeatedly test your system even after small changes (regression testing) � If a bug is found after development, a test is created to keep the bug from coming back � � TDD–13
Why TDD? � Programmers dislike testing � TDD–14
Why TDD? – 2 � Programmers dislike testing � They will test reasonably thoroughly the first time � The second time is less thorough � The third time ... ??? Good luck – testing is a boring task � TDD–15
Why TDD? – 3 � Programmers dislike testing � They will test reasonably thoroughly the first time � The second time is less thorough � The third time ... ??? Good luck – testing is a boring task � But programmers need to produce correct program text � So write the tests first � Make it easy to run the tests � TDD–16
Why TDD? – 3 � Encourages programmers to maintain an exhaustive set of repeatable tests � TDD–17
Why TDD? – 4 � Encourages programmers to maintain an exhaustive set of repeatable tests � Tests live alongside the class under test � Tests can be run frequently � After every single change with XP (extreme programming) � With tool support, tests can be run selectively � Making it reasonable to run relevant tests frequently � TDD–18
TDD Benefits � Fewer bugs � Program text can be refactored without fear � Continuous integration � During development a growing subset of the system always works � It may not do everything required but what it does do is right � Program text is more maintainable in that regression testing will find errors due to recent changes � TDD–19
XP approach to testing � The Extreme Programming approach � Follows TDD � Tests are written before the program text itself � If the program text has no automated test cases, it is assumed not to work � A testing framework is used so that automated testing can be done � TDD–20
XP approach to testing – 2 � So what is different? � Testing is done extremely frequently � After every change � This may be as often as every 5 or 10 minutes � TDD–21
XP approach to testing – 3 � So what is different? � Testing is done extremely frequently � After every change � This may be as often as every 5 or 10 minutes � A more balanced approach is to run tests frequently but after a coherent set of changes is made � TDD–22
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