Unit testing

In computer programming, unit testing is a test (often automated) that validates that individual units of source code are working properly. In Computer science, source code (commonly just source or code) is any sequence of statements or declarations written in some Human-readable A unit is the smallest testable part of an application. In procedural programming a unit may be an individual program, function, procedure, etc. Procedural programming can sometimes be used as a synonym for Imperative programming (specifying the steps the program must take to reach the desired state but can also , while in object-oriented programming, the smallest unit is a method, which may belong to a base/super class, abstract class or derived/child class. Object-oriented programming (OOP is a Programming paradigm that uses " objects " and their interactions to design applications and computer programs In Object-oriented programming, the term method refers to a Subroutine that is exclusively associated either with a class (called class methods

Ideally, each test case is independent from the others; Double objects like stubs, mock or fake objects^[1] as well as test harnesses can be used to assist testing a module in isolation. A test case in Software engineering is a set of conditions or variables under which a tester will determine if a Requirement or Use case upon In Object-oriented programming, mock objects are simulated objects that mimic the behavior of real objects in controlled ways In Object-oriented programming, mock objects are simulated objects that mimic the behavior of real objects in controlled ways In Software testing, a test harness or automated test framework is a collection of Software and test data configured to test a program unit by running it Unit testing is typically done by software developers to ensure that the code they have written meets software requirements and behaves as the developer intended. A software developer is a person or organization concerned with facets of the software development process wider than design and coding a somewhat broader scope of

1 Benefits
2 Separation of interface from implementation
3 Limitations of unit testing
4 Applications
5 See also
6 Notes
7 External links

Benefits

The goal of unit testing is to isolate each part of the program and show that the individual parts are correct. A unit test provides a strict, written contract that the piece of code must satisfy. As a result, it affords several benefits.

Facilitates change

Unit testing allows the programmer to refactor code at a later date, and make sure the module still works correctly (i. e. regression testing). Regression testing is any type of Software testing which seeks to uncover software regressions. The procedure is to write test cases for all functions and methods so that whenever a change causes a fault, it can be quickly identified and fixed. In Computer science, a subroutine ( function, method, procedure, or subprogram) is a portion of code within a larger In Object-oriented programming, the term method refers to a Subroutine that is exclusively associated either with a class (called class methods

Readily-available unit tests make it easy for the programmer to check whether a piece of code is still working properly. Good unit test design produces test cases that cover all paths through the unit with attention paid to loop conditions. Code coverage is a measure used in Software testing. It describes the degree to which the Source code of a program has been tested

In continuous unit testing environments, through the inherent practice of sustained maintenance, unit tests will continue to accurately reflect the intended use of the executable and code in the face of any change. Depending upon established development practices and unit test coverage, up-to-the-second accuracy can be maintained.

Simplifies integration

Unit testing helps to eliminate uncertainty in the units themselves and can be used in a bottom-up testing style approach. By testing the parts of a program first and then testing the sum of its parts, integration testing becomes much easier. 'Integration testing'(sometimes called Integration and Testing abbreviated I&T) is the phase of Software testing in which individual software modules are combined and tested

A heavily debated matter exists in assessing the need to perform manual integration testing. While an elaborate hierarchy of unit tests may seem to have achieved integration testing, this presents a false sense of confidence since integration testing evaluates many other objectives that can only be proven through the human factor. Some argue that given a sufficient variety of test automation systems, integration testing by a human test group is unnecessary. Test automation is the use of Software to control the execution of tests the comparison of actual outcomes to predicted outcomes the setting up of test preconditions Realistically, the actual need will ultimately depend upon the characteristics of the product being developed and its intended uses. Additionally, the human or manual testing will greatly depend on the availability of resources in the organization. Manual testing is the oldest and most rigorous type of Software testing.

Documentation

Unit testing provides a sort of living documentation of the system. Developers looking to learn what functionality is provided by a unit and how to use it can look at the unit tests to gain a basic understanding of the unit API.

Unit test cases embody characteristics that are critical to the success of the unit. A test case in Software engineering is a set of conditions or variables under which a tester will determine if a Requirement or Use case upon These characteristics can indicate appropriate/inappropriate use of a unit as well as negative behaviors that are to be trapped by the unit. A unit test case, in and of itself, documents these critical characteristics, although many software development environments do not rely solely upon code to document the product in development.

On the other hand, ordinary narrative documentation is more susceptible to drifting from the implementation of the program and will thus become outdated (e. g. design changes, feature creep, relaxed practices to keep documents up to date). Feature creep (or feeping creaturism) is the proliferation of features in a product such as Computer software.

Design

When software is developed using a test-driven approach, the Unit-Test may take the place of formal design. Each unit test can be seen as a design element specifying classes, methods, and observable behaviour. The following Java example will help illustrate this point.

Here is a test class that specifies a number of elements of the implementation. First, that there must be an interface called Adder, and an implementing class with a zero-argument constructor called AdderImpl. It goes on to assert that the Adder interface should have a method called add, with two integer parameters, which returns another integer. It also specifies the behaviour of this method for a small range of values.

 public class TestAdder {
   public void testSum() {
     Adder adder = new AdderImpl();
     assertTrue(adder. add(1,1) == 2);
     assertTrue(adder. add(1,2) == 3);
     assertTrue(adder. add(2,2) == 4);
     assertTrue(adder. add(0,0) == 0);
     assertTrue(adder. add(-1,-2) == -3);
     assertTrue(adder. add(-1,1) == 0);
     assertTrue(adder. add(1234,988) == 2222);
   }
 }

In this case the unit test, having been written first, acts as a design document specifying the form and behaviour of a desired solution, but not the implementation details, which are left as an exercise for the programmer. Following the 'do the simplest thing that could possibly work' practice, the easiest solution that will make the test pass is shown below.

 interface Adder {
   int add(int a, int b);
 }
 class AdderImpl implements Adder {
   int add(int a, int b) {
      return a + b;
   }
 }

Unlike other diagram-based design methods, using a unit-test as a design has one significant advantage. The design document (the unit-test itself) can be used to verify that the implementation adheres to the design. UML suffers from the fact that although a diagram may name a class Customer, the developer can call the class Wibble and nothing in the system would note this discrepancy. Unified Modeling Language ( UML) is a standardized general-purpose Modeling language in the field of Software engineering. With the unit-test design method, the tests will never pass if the developer does not implement the solution according to the design.

It is true that unit-testing lacks some of the accessibility of a diagram, but as UML diagrams are now easily generated for most modern languages by free tools (usually available as extensions to IDEs), it is hard to argue for the purchase of expensive UML design suites. Free tools, like those based on the xUnit framework, outsource to another system the graphical rendering of a view for human consumption. Various code-driven testing frameworks have come to be known collectively as XUnit.

Separation of interface from implementation

Because some classes may have references to other classes, testing a class can frequently spill over into testing another class. In Computer science, a reference is an object containing information which refers to data stored elsewhere as opposed to containing the data itself A common example of this is classes that depend on a database: in order to test the class, the tester often writes code that interacts with the database. A Computer Database is a structured collection of records or data that is stored in a computer system This is a mistake, because a unit test should never go outside of its own class boundary. Instead, the software developer should create an abstract interface around the database connection, and then implement that interface with their own mock object. In Object-oriented programming, mock objects are simulated objects that mimic the behavior of real objects in controlled ways By abstracting this necessary attachment from the code (temporarily reducing the net effective coupling), the independent unit can be more thoroughly tested than may have been previously achieved. This results in a higher quality unit that is also more maintainable.

Limitations of unit testing

Testing cannot be expected to catch every error in the program. The same is true for unit testing. By definition, unit testing only tests the functionality of the units themselves. Therefore, it may not catch integration errors, performance problems, or other system-wide issues. Performance Testing covers a broad range of engineering or functional evaluations where a material product system or person is not specified by detailed material or component Specifications Unit testing is more effective if it is used in conjunction with other software testing activities. Software testing is an Empirical investigation conducted to provide stakeholders with information about the quality of the product or service under test, with respect to the Like all forms of software testing, unit tests can only show the presence of errors; it cannot show the absence of errors.

Software testing is a combinatorial problem. For example, every boolean decision statement requires at least two tests: one with an outcome of "true" and one with an outcome of "false". As a result, for every line of code written, programmers often need 3 to 5 lines of test code. ^[2]

To obtain the intended benefits from unit testing, a rigorous sense of discipline is needed throughout the software development process. It is essential to keep careful records not only of the tests that have been performed, but also of all changes that have been made to the source code of this or any other unit in the software. Use of a version control system is essential. Revision control (also known as version control (system (VCS, source control or (source code management (SCM) is the management of multiple revisions If a later version of the unit fails a particular test that it had previously passed, the version-control software can provide a list of the source code changes (if any) that have been applied to the unit since that time.

It is also essential to implement a sustainable process for ensuring that test case failures are reviewed daily and addressed immediately. ^[3] If such a process is not implemented and ingrained into the team's workflow, the application will evolve out of sync with the unit test suite ― increasing false positives and reducing the effectiveness of the test suite.

Applications

Extreme Programming

Unit testing is the cornerstone of Extreme Programming (XP), which relies on an automated unit testing framework. Extreme Programming (or XP) is a Software engineering methodology (and a form of Agile software development) Proponents of Extreme Programming and agile This page is a list of tables of code-driven Unit testing frameworks for various Programming languages Some of these are based on XUnit, but not all of them are This automated unit testing framework can be either third party, e. g. xUnit, or created within the development group. Various code-driven testing frameworks have come to be known collectively as XUnit.

Extreme Programming uses the creation of unit tests for test-driven development. Test-Driven Development (TDD is a Software development technique consisting of short iterations where new Test cases covering the desired improvement or The developer writes a unit test that exposes either a software requirement or a defect. This test will fail because either the requirement isn't implemented yet, or because it intentionally exposes a defect in the existing code. Then, the developer writes the simplest code to make the test, along with other tests, pass.

Most code in a system is unit tested, but not necessarily all paths through the code. XP mandates a 'test everything that can possibly break' strategy, over the tradition 'test every execution path' method. This leads XP developers to develop fewer tests than classical methods, but this isn't really a problem, more a restatement of fact, as classical methods have rarely ever been followed methodically enough for all execution paths to have been thoroughly tested. XP simply recognises that testing is rarely exhaustive (because often that is too expensive and time consuming to be economically viable), and provides guidance on how to effectively focus the limited resources we can afford expend on the problem.

Crucially, the test code is considered a first class project artefact in that it is maintained at the same quality as the implementation code, with all duplication removed. Developers release unit testing code to the code repository in conjunction with the code it tests. XP's thorough unit testing allows the benefits mentioned above, such as simpler and more confident code development and refactoring, simplified code integration, accurate documentation, and more modular designs. These unit tests are also constantly run as a form of regression test. Regression testing is any type of Software testing which seeks to uncover software regressions.

Techniques

Unit testing is commonly automated, but may still be performed manually. Test automation is the use of Software to control the execution of tests the comparison of actual outcomes to predicted outcomes the setting up of test preconditions The IEEE does not favor one over the other. The Institute of Electrical and Electronics Engineers or IEEE (read eye-triple-e) is an international Non-profit, professional organization ^[4] A manual approach to unit testing may employ a step-by-step instructional document. Nevertheless, the objective in unit testing is to isolate a unit and validate its correctness. Automation is efficient for achieving this, and enables the many benefits listed in this article. Conversely, if not planned carefully, a careless manual unit test case may execute as an integration test case that involves many software components, and thus preclude the achievement of most if not all of the goals established for unit testing.

Under the automated approach, to fully realize the effect of isolation, the unit or code body subjected to the unit test is executed within a framework outside of its natural environment, that is, outside of the product or calling context for which it was originally created. This page is a list of tables of code-driven Unit testing frameworks for various Programming languages Some of these are based on XUnit, but not all of them are Testing in an isolated manner has the benefit of revealing unnecessary dependencies between the code being tested and other units or data spaces in the product. These dependencies can then be eliminated.

Using an automation framework, the developer codes criteria into the test to verify the correctness of the unit. During execution of the test cases, the framework logs those that fail any criterion. Many frameworks will also automatically flag and report in a summary these failed test cases. Depending upon the severity of a failure, the framework may halt subsequent testing.

As a consequence, unit testing is traditionally a motivator for programmers to create decoupled and cohesive code bodies. In Computer science, coupling or dependency is the degree to which each program module relies on each one of the other modules In Computer programming, cohesion is a measure of how strongly-related and focused the various responsibilities of a software module are This practice promotes healthy habits in software development. Design patterns, unit testing, and refactoring often work together so that the most ideal solution may emerge. In Software engineering, a design pattern is a general reusable solution to a commonly occurring problem in Software design.

Unit testing frameworks

Unit testing frameworks, which help simplify the process of unit testing, have been developed for a wide variety of languages. This page is a list of tables of code-driven Unit testing frameworks for various Programming languages Some of these are based on XUnit, but not all of them are It is generally possible to perform unit testing without the support of specific framework by writing client code that exercises the units under test and uses assertion, exception, or early exit mechanisms to signal failure. This approach is valuable in that there is a non-negligible barrier to the adoption of unit testing. However, it is also limited in that many advanced features of a proper framework are missing or must be hand-coded.

Notes

^ Fowler, Martin (2007-01-02). Martin Fowler is an author and international speaker on software architecture specializing in object-oriented analysis and design UML, patterns, and Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 366 - The Alamanni cross the frozen Rhine River in large numbers invading the Roman Empire. Mocks aren't Stubs. Retrieved on 2008-04-01. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 527 - Byzantine Emperor Justin I names his nephew Justinian I as co-ruler and successor to the throne
^ Cramblitt, Bob (2007-09-20). Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 451 - The Battle of Chalons takes place in North Eastern France. Alberto Savoia sings the praises of software testing. Retrieved on 2007-11-29. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1777 - San Jose California, is founded as el Pueblo de San José de Guadalupe
^ daVeiga, Nada (2008-02-06). 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 46 BC - Julius Caesar defeats the combined army of Pompeian followers and Numidians under Metellus Scipio Change Code Without Fear: Utilize a regression safety net. Retrieved on 2008-02-08. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 421 - Constantius III becomes co- Emperor of the Western Roman Empire.
^ IEEE Standards Board, "IEEE Standard for Software Unit Testing: An American National Standard, ANSI/IEEE Std 1008-1987" in IEEE Standards: Software Engineering, Volume Two: Process Standards; 1999 Edition; published by The Institute of Electrical and Electronics Engineers, Inc. Software Engineering Technical Committee of the IEEE Computer Society.

External links

The evolution of Unit Testing Syntax and Semantics

Dictionary

-noun

(computing) A software testing methodology in which individual tests (unit tests) are developed for each small part of a program.

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