Unit tests vs Functional tests

Question

What is the difference between unit tests and functional tests  Can a unit test also test a function

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A unit test tests an independent unit of behavior  What is a unit of behavior  It s the smallest piece of the system that can be independently unit tested   This definition is actually circular  IOW it s really not a definition at all  but it seems to work quite well in practice  because you can sort-of understand it intuitively   A functional test tests an independent piece of functionality       A unit of behavior is very small  while I absolutely dislike this stupid  one unit test per method  mantra  from a size perspective it is about right  A unit of behavior is something between a part of a method and maybe a couple of methods  At most an object  but not more than one  A piece of functionality usually comprises many methods and cuts across several objects and often through multiple architectural layers       A unit test would be something like  when I call the validate country code   function and pass it the country code  ZZ  it should return false  A functional test would be  when I fill out the shipping form with a country code of ZZ  I should be redirected to a help page which allows me to pick my country code out of a menu       Unit tests are written by developers  for developers  from the developer s perspective  Functional tests may be user facing  in which case they are written by developers together with users  or maybe with the right tools and right users even by the users themselves   for users  from the user s perspective  Or they may be developer facing  e g  when they describe some internal piece of functionality that the user doesn t care about   in which case they are written by developers  for developers  but still from the user s perspective       In the former case  the functional tests may also serve as acceptance tests and as an executable encoding of functional requirements or a functional specification  in the latter case  they may also serve as integration tests  Unit tests change frequently  functional tests should never change within a major release

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The way I think of it is like this  A unit test establishes that the code does what you intended the code to do  e g  you wanted to add parameter a and b  you in fact add them  and don t subtract them   functional tests test that all of the code works together to get a correct result  so that what you intended the code to do in fact gets the right result in the system

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Functional test  does not mean you are testing a function  method  in your code   It means  generally  that you are testing system functionality -- when I run foo file txt at the command line  the lines in file txt become reversed  perhaps   In contrast  a single unit test generally covers a single case of a single method -- length  hello   should return 5  and length  hi   should return 2   See also IBM s take on the line between unit testing and functional testing

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AFAIK  unit testing is NOT functional testing  Let me explain with a small example  You want to test if the login functionality of an email web app is working or not  just as a user would  For that  your functional tests should be like this   1- existing email  wrong password - gt  login page should show error  wrong password   2- non-existing email  any password - gt  login page should show error  no such email   3- existing email  right password - gt  user should be taken to his inbox page  4- no  symbol in email  right password - gt  login page should say  errors in form  please fix them      Should our functional tests check if we can login with invalid inputs   Eg  Email has no   symbol  username has more than one dot  only one dot is permitted    com appears before   etc    Generally  no   That kind of testing goes into your unit tests   You can check if invalid inputs are rejected inside unit tests as shown in the tests below   class LoginInputsValidator   method validate inputs values email  password      1-If email is not like string string myapp com  then throw error      2-If email contains abusive words  then throw error      3-If password is less than 10 chars  throw error    Notice that the functional test 4 is actually doing what unit test 1 is doing  Sometimes  functional tests can repeat some  not all  of the testing done by unit tests  for different reasons  In our example  we use functional test 4 to check if a particular error message appears on entering invalid input  We don t want to test if all bad inputs are rejected or not  That is the job of unit tests

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TLDR   To answer the question  Unit Testing is a subtype of Functional Testing     There are two big groups  Functional and Non-Functional Testing  The best  non-exhaustive  illustration that I found is this one  source  www inflectra com          1  Unit Testing  testing of small snippets of code  functions methods   It may be considered as  white-box  functional testing    When functions are put together  you create a module   a standalone piece  possibly with a User Interface that can be tested  Module Testing   Once you have at least two separate modules  then you glue them together and then comes       2  Integration Testing  when you put two or more pieces of  sub modules or  sub systems together and see if they play nicely together    Then you integrate the 3rd module  then the 4th and 5th in whatever order you or your team see fit  and once all the jigsaw pieces are placed together  comes      3  System Testing  testing SW as a whole  This is pretty much  Integration testing of all pieces together      If that s OK  then comes      4  Acceptance Testing  did we build what the customer asked for actually  Of course  Acceptance Testing should be done throughout the lifecycle  not just at the last stage  where you realise that the customer wanted a sportscar and you built a van

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The basic distinction  though  is that functional tests test the application from the outside  from the point of view of the user  Unit tests test the application from the inside  from the point of view of the programmer  Functional tests should help you build an application with the right functionality  and guarantee you never accidentally break it  Unit tests should help you to write code that   s clean and bug free   Taken from  Python TDD  book by Harry Percival

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UNIT TESTING  Unit testing includes testing of smallest unit of code which usually are functions or methods  Unit testing is mostly done by developer of unit method function  because they understand the core of a  function  The main goal of the developer is to cover code by unit tests   It has a limitation that some functions cannot be tested through unit tests  Even after the successful completion of all the unit tests  it does not guarantee correct operation of the product  The same function can be used in few parts of the system while the unit test was written only for one usage   FUNCTIONAL TESTING  It is a type of Black Box testing where testing will be done on the functional aspects of a product without looking into the code  Functional testing is mostly done by a dedicated Software tester  It will include positive  negative and BVA techniques using un standardized data for testing the specified functionality of product  Test coverage is conducted in an improved manner by functional tests than by unit tests  It uses application GUI for testing  so it   s  easier to determine what exactly a specific part of the interface is responsible for rather to determine what a code is function responsible for

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In Rails  the unit folder is meant to hold tests for your models  the functional folder is meant to hold tests for your controllers  and the integration folder is meant to hold tests that involve any number of controllers interacting  Fixtures are a way of organizing test data  they reside in the fixtures folder  The test helper rb file holds the default configuration for your tests  u can visit this

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According to ISTQB those two are not comparable  Functional testing is not integration testing   Unit test is one of tests level and functional testing is type of testing   Basically      The function of a system  or component  is  what it does   This is   typically described in a requirements specification  a functional   specification  or in use cases    while     Component testing  also known as unit  module and program testing    searches for defects in  and verifies the functioning of software    e g  modules  programs  objects  classes  etc   that are separately   testable    According to ISTQB component unit test can be functional or not-functional      Component testing may include testing of functionality and specific non-functional characteristics such as resource-behavior  e g  memory leaks   performance or robustness testing  as well as structural testing  e g  decision coverage     Quotes from Foundations of software testing - ISTQB certification

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Unit Tests are written from a programmers or developers perspective  They are made to ensure that a particular method  or a unit  of a class performs a set of specific tasks  Functional Tests are written from the user s perspective  They ensure that the system is functioning as users are expecting it to

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My vision is  Unit testing  In Procedural programming unit is a procedure  in Object oriented programming unit is a class  Unit is isolated and reflects a developer perspective Functional testing - more than Unit  User perspective  which describes a feature  use case  story     Integration testing - check if all separately developed components work together  It can be other application  service  library  database  network etc   Narrow integration test - double About  is used  The main purpose is to check if component is configured in a right way Broad integration test  End to End test  System test  - live version  The main purpose is to check if all components are configured in a right way   UI testing - checks if user input triggers a correct action and the UI is changed when some actions are happened       Non functional testing - other cases  Performance testing - calculate a speed and other metrics Usability testing - UX

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Unit testing is usually done by developers  The objective of doing the same is to make sure their code works properly  General rule of thumb is to cover all the paths in code using unit testing   Functional Testing  This is a good reference  Functional Testing Explanation

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Unit tests tell a developer that the code is doing things right  functional tests tell a developer that the code is doing the right things   You can read more at Unit Testing versus Functional Testing  A well explained real-life analogy of unit testing and functional testing can be described as follows   Many times the development of a system is likened to the building of a house  While this analogy isn t quite correct  we can extend it for the purposes of understanding the difference between unit and functional tests  Unit testing is analogous to a building inspector visiting a house s construction site  He is focused on the various internal systems of the house  the foundation  framing  electrical  plumbing  and so on  He ensures  tests  that the parts of the house will work correctly and safely  that is  meet the building code  Functional tests in this scenario are analogous to the homeowner visiting this same construction site  He assumes that the internal systems will behave appropriately  that the building inspector is performing his task  The homeowner is focused on what it will be like to live in this house  He is concerned with how the house looks  are the various rooms a comfortable size  does the house fit the family s needs  are the windows in a good spot to catch the morning sun  The homeowner is performing functional tests on the house  He has the user s perspective  The building inspector is performing unit tests on the house  He has the builder s perspective    As a summary  Unit Tests are written from a programmers perspective  They are made to ensure that a particular method  or a unit  of a class performs a set of specific tasks  Functional Tests are written from the user s perspective  They ensure that the system is functioning as users are expecting it to

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Unit Test - testing an individual unit  such as a method  function  in a class  with all dependencies mocked up    Functional Test - AKA Integration Test  testing a slice of functionality in a system  This will test many methods and may interact with dependencies like Databases or Web Services

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very simply we can say     black box  user interface test like functional test white box  code test like unit test    read more here

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Unit Test - Unit testing is particularly used to test the product component by component specially while the product is under development  Junit and Nunit type of tools will also help you to test the product as per the Unit    Rather than solving the issues after the Integration it is always comfortable to get it resolved early in the development   Functional Testing - As for as the Testing is concerned there are two main types of Testing as  1 Functional Test 2 Non-Functional Test   Non-Functional Test is a test where a Tester will test that The product will perform all those quality attributes that customer doesn t mention but those quality attributes should be there  Like -Performance Usability Security Load Stress etc  but in the Functional Test - The customer is already present with his requirements and those are properly documented The testers task is to Cross check that whether the Application Functionality is performing according to the Proposed System or not  For that purpose Tester should test for the Implemented functionality with the proposed System

[unit-testing] Unit tests vs Functional tests

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