What is unit testing and how do you do it

Question

Exact duplicate of many posts   What is unit testing   What Makes a Good Unit Test   New to Unit Testing  Unit Testing - definitions  Learning Unit Testing  How to properly mock and unit test  Unit Testing  Beginner Questions  And many more      Also  Google for site stackoverflow com  how do you  unit-test  I have read some questions on unit testing  but I don t exactly know WHAT it is or how you do it  I was hoping if someone can tell me the following    What exactly IS unit testing  Is it built into code or run as separate programs  Or something else  How do you do it  When should it be done  Are there times or projects not to do it  Is everything unit-testable    Thanks a lot for the help

User · Answer

What     A methodology for automaticaly testing code against a battery of tests  designed to enforce desired outcomes and manage change    A  unit  in this sense is the smallest atomic component of the code that makes sense to test  typically a method of some class for example  Part of this process is building up stub objects  or  mocks   which allow you to work with a unit as an independant object   How     Almost always  the process of unit-testing is built into an IDE  or through extensions  such that it executes the tests with every compile  A number of frameworks exist for assisting the creation of unit tests  and indeed mock objcts   often named fooUnit  cf  jUnit  xUnit  nUnit   These frameworks provide a formalised way to create tests    As a process  test driven development  TDD  is often the motivation for unit testing  but unit testing does not require TDD  which supposes that the tests are a part of the spec definition  and therefore requires that they are written first  with code only written to  solve  these tests   When     Almost always  Very small  throwaway projects may not be worth it  but only if you re quite sure they really are throwaway  In theory every object orientated program is unit testable  but some design pattrns make this difficult  Notoriously  the singleton pattern is problematic  where conversely dependancy injection frameworks are very much unit testing oriented

User · Answer

Unit testing involves breaking your program into pieces  and subjecting each piece to a series of tests   Usually tests are run as separate programs  but the method of testing varies  depending on the language  and type of software  GUI  command-line  library     Most languages have unit testing frameworks  you should look into one for yours   Tests are usually run periodically  often after every change to the source code  The more often the better  because the sooner you will catch problems

User · Answer

On the  How to do it  part   I think the introduction to ScalaTest does good job of illustrating different styles of unit tests   On the  When to do it  part   Unit testing is not only for testing  By doing unit testing you also force the design of the software into something that is unit testable  Many people are of the opinion that this design is for the most part Good Design TM  regardless of other benefits from testing   So one reason to do unit test is to force your design into something that hopefully will be easier to maintain that what it would be had you not designed it for unit testing

User · Answer

What is unit testing   Unit testing simply verifies that individual units of code  mostly functions  work as expected  Usually you write the test cases yourself  but some can be automatically generated   The output from a test can be as simple as a console output  to a  green light  in a GUI such as NUnit  or a different language-specific framework   Performing unit tests is designed to be simple  generally the tests are written in the form of functions that will determine whether a returned value equals the value you were expecting when you wrote the function  or the value you will expect when you eventually write it - this is called Test Driven Development when you write the tests first    How do you perform unit tests   Imagine a very simple function that you would like to test   int CombineNumbers int a  int b        return a b      The unit test code would look something like this   void TestCombineNumbers         Assert IsEqual CombineNumbers 5  10   15      Assert is an object that is part of your test framework     Assert IsEqual CombineNumbers 1000  -100   900       When you run the tests  you will be informed that these tests have passed  Now that you ve built and run the tests  you know that this particular function  or unit  will perform as you expect   Now imagine another developer comes along and changes the CombineNumbers   function for performance  or some other reason   int CombineNumbers int a  int b        return a   b      When the developer runs the tests that you have created for this very simple function  they will see that the first Assert fails  and they now know that the build is broken   When should you perform unit tests   They should be done as often as possible  When you are performing tests as part of the development process  your code is automatically going to be designed better than if you just wrote the functions and then moved on  Also  concepts such as Dependency Injection are going to evolve naturally into your code   The most obvious benefit is knowing down the road that when a change is made  no other individual units of code were affected by it if they all pass the tests

User · Answer

I find the easiest way to illustrate it is to look at some code  This getting started page on the NUnit site is a good introduction to the what and the how  http   www nunit org index php p quickStart amp r 2 5  Is everything testable  Generally if it calculates something then yes  UI code is a whole other problem to deal with though  as simulating users clicking on buttons is tricky   What should you test  I tend to write tests around the things I know are going to be tricky  Complicated state transitions  business critical calculations  that sort of thing  Generally I m not too worried about testing basic input output stuff  although the purists will doubtless say I m wrong on that front and everything should be tested  Like so many other things  there is no right answer

User · Answer

What is unittesting  It is tricky to define  On a technical level  you build functions that call functions in your codebase and validate the results  Basically  you get a bunch of things like  assert 5 3     8   just more complicated  as in DataLayer MockDatabase    getUser   name     Dilbert     On a tool-view-level  you add an automated  project-specific check if everything still works like you assumed things worked  This is very  very helpful if you refactor and if you implement complicated algorithms   The result generally is a bunch of documentation and a lot less bugs  because the behaviour of the code is pinned down   I build test cases for all the edge cases and run them similar to the workings of a generational garbage collector  While I implement a class  I only run the test cases that involve the class  Once I am done with working on that class  I run all unittests in order to see if everything still works   You should test as much as possible  as long as the test code is easy enough to stay untested  Given that  no  not everything is testable in a sane way  Think User interfaces  Think a driver for a space shuttle or a nuclear bomb  at least not with pure JUnit-tests       However  lots and lots of code is testable  Datastructures are  Algorithms are  Most Applicationlogic-classes are  So test it   HTH  tetha

User · Answer

What exactly IS unit testing  Is it   built into code or run as separate   programs  Or something else    From MSDN  The primary goal of unit testing is to take the smallest piece of testable software in the application  isolate it from the remainder of the code  and determine whether it behaves exactly as you expect   Essentially  you are writing small bits of code to test the individual bits of your code  In the  net world  you would run these small bits of code using something like NUnit or MBunit or even the built in testing tools in visual studio  In Java you might use JUnit  Essentially the test runners will build your project  load and execute the unit tests and then let you know if they pass or fail      How do you do it    Well it s easier said than done to unit test  It takes quite a bit of practice to get good at it  You need to structure your code in a way that makes it easy to unit test to make your tests effective       When should it be done  Are there times or projects not to do it  Is   everything unit-testable    You should do it where it makes sense  Not everything is suited to unit testing  For example UI code is very hard to unit test and you often get little benefit from doing so  Business Layer code however is often very suitable for tests and that is where most unit testing is focused   Unit testing is a massive topic and to fully get an understanding of how it can best benefit you I d recommend getting hold of a book on unit testing such as  Test Driven Development by Example  which will give you a good grasp on the concepts and how you can apply them to your code

[unit-testing] What is unit testing and how do you do it?

Examples related to unit-testing