DOCSLIB.ORG

Mock Objects

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Mock Objects software construction Editors: Andy Hunt and Dave Thomas I The Pragmatic Programmers [email protected] I [email protected] Mock Objects Dave Thomas and Andy Hunt Yet sit and see; Minding true things by what their mockeries be. —Shakespeare, Henry V ne thing that makes unit-testing code drop off, and we all know where that leads. so hard is the way the real world Fortunately there’s a testing pattern that keeps intruding. If all we had to do can help. Using mock objects, you can test was code up tests for methods that code in splendid isolation, simulating all sort arrays or generate Fibonacci se- those messy real-world things that would O ries, life would be easy. But in the real otherwise make automated testing impossi- world we have to test code that uses data- ble. And, as with many other testing prac- bases, communications devices, user inter- tices, the discipline of using mock objects faces, and external applications. We might can improve your code’s structure. An example: Testing a servlet Servlets are chunks of code that a Web server manages. Requests to certain URLs are forwarded to a servlet container (or man- ager) such as Jakarta Tomcat (http://jakarta. apache.org/tomcat), which in turn invokes the servlet code. The servlet then builds a re- sponse that it sends back to the requesting browser. From the end user’s perspective, it’s just like accessing any other page. Figure 1 shows part of the source of a have to interface to devices that aren’t yet trivial servlet that converts temperatures available or simulate network errors that are from Fahrenheit to Celsius. Let’s quickly impossible to generate locally. This all con- step through its operation. When the servlet spires to stop our unit tests from being neat, container receives the request, it automati- self-contained (and orthogonal) chunks of cally invokes the servlet method doGet(), code. Instead, if we’re not careful, we find passing in two parameters, a request and a ourselves writing tests that end up initializ- response. (These are important for our test- ing nearly every system component just to ing later). The request parameter contains give the tests enough context to run. Not information about the request; the servlet’s only is this time consuming, it also intro- job is to fill in the response. The servlet’s duces a ridiculous amount of coupling into body gets the contents of the field “Fahren- the testing process: someone changes an in- heit” from the request, converts it to Cel- terface or a database table, and suddenly the sius, and writes the results back to the user. setup code for your poor little unit test dies The writing is done via a PrintWriter object, mysteriously. Even the best-intentioned de- which a factory method in the response ob- velopers become discouraged after this hap- ject provides. If an error occurs converting pens a few times. Eventually, testing starts to the number (perhaps the user typed “boo!” 22 IEEE SOFTWARE May/June 2002 0740-7459/02/$17.00 © 2002 IEEE SOFTWARE CONSTRUCTION into the form’s temperature field), we 1 public void doGet(HttpServletRequest req, catch the exception and report the er- 2 HttpServletResponse res) ror in the response. 3 throws ServletException, IOException Having written this code (or be- 4{ fore writing it, for those in the Ex- 5 String str_f = req.getParameter(“Fahrenheit”); treme Programming tribe), we’ll want 6 7 res.setContentType(“text/html”); a unit test to verify it. This is where 8 PrintWriter out = res.getWriter(); things start looking difficult. This 9 snippet of code runs in a fairly com- 10 try { plex environment (a Web server and a 11 int temp_f = Integer.parseInt(str_f); servlet container), and it requires a 12 double temp_c = (temp_f – 32) * 5.0 / 9.0; user sitting at a browser to interact 13 out.println(“Fahrenheit: “ + temp_f + with it. This is hardly the basis of a “, Celsius: “ + temp_c); 14 } good automated unit test. 15 catch (NumberFormatException e) { But let’s look at our servlet code 16 out.println(“Invalid temperature: “ + str_f); again. Its interface is pretty simple: as 17 } we mentioned before, it receives two 18 } parameters, a request and a response. The request object must be able to Figure 1. A trivial servlet that converts temperatures from provide a reasonable string when its Fahrenheit to Celsius. getParameter() method is called, and the response object must support I The real object has nondeterminis- We can use mock objects in two dis- setContentType() and getWriter(). tic behavior. tinct ways. First, we can use them to It’s starting to look as if we might be I The real object is difficult to set up. set up an environment in which our able to write some stubs: objects that I The real object has behavior that test code runs: we can initialize values pretend to be real request and response is hard to trigger (for example, a in the objects that the method under objects but that contain just enough network error). test uses. Figure 2 shows a typical set logic to let us run our code. In principle I The real object is slow. of tests using the JUnit testing frame- this is easy: both HttpServletRequest I The real object has (or is) a user work, which is available at www.junit. and HttpServletResponse are inter- interface. org. We use a MockHttpServletRe- faces, so all we have to do is whip up a I The test needs to ask the real ob- quest object to set up the context in couple of classes that implement the in- ject about how it was used (for ex- which to run the test. On line six of the terfaces and we’re set. Unfortunately, ample, a test might need to check code, we set the parameter “Fahren- when we look at the interface, we dis- to see that a callback function was heit” to the value “boo!” in the re- cover that we’ll need to implement actually called). quest object. This is equivalent to the dozens of methods just to get the thing I The real object does not yet exist. user entering “boo!” in the corre- to compile. Fortunately, other folks sponding form field; our mock object have already done the work for us. Mackinnon, Freeman, and Craig eliminates the need for human input also developed the code for a mock ob- when the test runs. Mock objects ject framework for Java programmers Mock objects can also verify that Tim Mackinnon, Steve Freeman, (available at www.mockobjects.com). actions were taken. On line seven of and Philip Craig introduced the con- Let’s use that code to test our servlet. Figure 2, we tell the response object cept of mock objects in their paper The good news is that in addition that we expect the method under test “Endo-Testing: Unit Testing with to the underlying framework code, the to set the response’s content type to Mock Objects” (www.cs.ualberta.ca/ mockobjects package comes with a text/html. Then, on lines 9 and 22, ~hoover/cmput401/XP-Notes/xp-conf/ number of mocked-up application-level after the method under test has run, Papers/4_4_MacKinnon.pdf), which objects. You’ll find mock output objects we tell the response object to verify they presented at XP2000. Their idea (OutputStream, PrintStream, and that this happened. Here, the mock is a natural extension of the ad hoc PrintWriter), objects that mock the object eliminates the need for a hu- stubbing that testers have been doing java.sql library, and classes for fak- man to check the result visually. This all along. The difference is that they ing out a servlet environment. In par- example shows a pretty trivial verifi- describe a framework to make writ- ticular, the package provides mocked- cation: in reality, mock objects can ing mock objects and incorporating up versions of HttpServletRequest verify that fairly complex sequences them into unit testing easier. and HttpServletResponse, which by of actions have been performed. Their paper lists seven good rea- an incredible coincidence are the types Mock objects can also record the sons to use a mock object (para- of the parameters of the method we data that was given to them. In our phrased slightly here): want to test. case, the response object receives the May/June 2002 IEEE SOFTWARE 23 SOFTWARE CONSTRUCTION 1 public void test_bad_parameter() throws Exception { hoc basis, coding up stubs when we 2 TemperatureServlet s = new TemperatureServlet(); needed them. However, we 3 MockHttpServletRequest request = personally have recently started new MockHttpServletRequest(); benefiting from adopting a more 4 MockHttpServletResponse response = systematic approach to creating new MockHttpServletResponse(); mock objects. Even things as simple 5 as consistent naming schemes have 6 request.setupAddParameter(“Fahrenheit”, “boo!”); helped make our tests more readable 7 response.setExpectedContentType(“text/html”); and the mock objects themselves more 8 s.doGet(request, response); portable from project to project. 9 response.verify(); There are several mock object frame- 10 assertEquals(“Invalid temperature: boo!\r\n”, works to choose from. Three for Java 11 response.getOutputStreamContents()); are at www.c2.com/cgi/wiki?MockOb- 12 } ject, and a fine implementation for Ruby 13 is at www.b13media.com/dev/ruby/ 14 public void test_boil() throws Exception { mock.html. If the thought of writing 15 TemperatureServlet s = new TemperatureServlet(); all the mock object classes you might 16 MockHttpServletRequest request = new MockHttpServletRequest(); need is intimidating, look at Easy- 17 MockHttpServletResponse response = Mock (www.easymock.org), a con- new MockHttpServletResponse(); venient Java API for creating mock 18 objects dynamically.
Load more

Recommended publications
  • From Zero to 1000 Tests in 6 Months
    From Zero to 1000 tests in 6 months Or how not to lose your mind with 2 week iterations Name is Max Vasilyev Senior Developer and QA Manager at Solutions Aberdeen http://tech.trailmax.info @trailmax Business Does Not Care • Business does not care about tests. • Business does not care about internal software quality. • Business does not care about architecture. • Some businesses don’t care so much, they even don’t care about money. Don’t Tell The Business Just do it! Just write your tests, ask no one. Honestly, tomorrow in the office just create new project, add NUnit package and write a test. That’ll take you 10 minutes. Simple? Writing a test is simple. Writing a good test is hard. Main questions are: – What do you test? – Why do you test? – How do you test? Our Journey: Stone Age Started with Selenium browser tests: • Recording tool is OK to get started • Boss loved it! • Things fly about on the screen - very dramatic But: • High maintenance effort • Problematic to check business logic Our Journey: Iron Age After initial Selenium fever, moved on to integration tests: • Hook database into tests and part-test database. But: • Very difficult to set up (data + infrastructure) • Problematic to test logic Our Journey: Our Days • Now no Selenium tests • A handful of integration tests • Most of the tests are unit-ish* tests • 150K lines of code in the project • Around 1200 tests with 30% coverage** • Tests are run in build server * Discuss Unit vs Non-Unit tests later ** Roughly 1 line of test code covers 2 lines of production code Testing Triangle GUI Tests GUI Tests Integration Tests Integration Tests Unit Tests Unit Tests Our Journey: 2 Week Iterations? The team realised tests are not optional after first 2-week iteration: • There simply was no time to manually test everything at the end of iteration.
    [Show full text]
  • Designpatternsphp Documentation Release 1.0
    DesignPatternsPHP Documentation Release 1.0 Dominik Liebler and contributors Jul 18, 2021 Contents 1 Patterns 3 1.1 Creational................................................3 1.1.1 Abstract Factory........................................3 1.1.2 Builder.............................................8 1.1.3 Factory Method......................................... 13 1.1.4 Pool............................................... 18 1.1.5 Prototype............................................ 21 1.1.6 Simple Factory......................................... 24 1.1.7 Singleton............................................ 26 1.1.8 Static Factory.......................................... 28 1.2 Structural................................................. 30 1.2.1 Adapter / Wrapper....................................... 31 1.2.2 Bridge.............................................. 35 1.2.3 Composite............................................ 39 1.2.4 Data Mapper.......................................... 42 1.2.5 Decorator............................................ 46 1.2.6 Dependency Injection...................................... 50 1.2.7 Facade.............................................. 53 1.2.8 Fluent Interface......................................... 56 1.2.9 Flyweight............................................ 59 1.2.10 Proxy.............................................. 62 1.2.11 Registry............................................. 66 1.3 Behavioral................................................ 69 1.3.1 Chain Of Responsibilities...................................
    [Show full text]
  • Stream-Based Verification with Junit
    Stream-Based Verification with JUnit Strombasierte Verifikation mit JUnit Masterarbeit Im Rahmen des Studiengangs Vorgelegt von Ausgegeben und betreut von Informatik Denis-Michael Lux Prof. Dr. Martin Leucker der Universität zu Lübeck mit Unterstützung von Malte Schmitz, M.Sc. Dipl.-Inf. Daniel Thoma Lübeck, den 14. Juni 2019 Selbstständigkeitserklärung Der Verfasser versichert an Eides statt, dass er die vorliegende Arbeit selbständig, ohne fremde Hilfe und ohne Benutzung anderer als der angegebenen Hilfsmittel angefertigt hat. Die aus fremden Quellen (einschließlich elektronischer Quellen) direkt oder indirekt über- nommenen Gedanken sind ausnahmslos als solche kenntlich gemacht. Die Arbeit ist in gle- icher oder ähnlicher Form oder auszugsweise im Rahmen einer anderen Prüfung noch nicht vorgelegt worden. Ort/Datum Unterschrift des Verfassers Contents Introduction 1 1 Unit Testing and Mocking in JUnit 3 1.1 Unit Testing ................................... 4 1.2 The JUnit Testing Framework ......................... 4 1.3 Assertions .................................... 8 1.4 Mocks and Stubs ................................ 10 2 Stream Runtime Verification 13 2.1 Runtime Verfication .............................. 13 2.2 Stream Processing ............................... 14 2.3 Temporal Stream-based Specification Language (TeSSLa) .......... 20 3 TeSSLa-Based Monitoring and Mocking in JUnit 25 3.1 Application Code Instrumentation ...................... 25 3.2 Monitors for Test Cases and Test Suites .................... 28 3.3 Class and Interface
    [Show full text]
  • Autonomic Test Case Generation of Failing Code Using AOP By
    Autonomic Test Case Generation of Failing Code Using AOP by Giovanni Murguia B.Sc., Instituto Tecnol´ogicoy de Estudios Superiores de Monterrey, Mexico 2008 A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in the Department of Computer Science c Giovanni Murguia, 2020 University of Victoria All rights reserved. This thesis may not be reproduced in whole or in part, by photocopying or other means, without the permission of the author. ii Autonomic Test Case Generation of Failing Code Using AOP by Giovanni Murguia B.Sc., Instituto Tecnol´ogicoy de Estudios Superiores de Monterrey, Mexico 2008 Supervisory Committee Dr. Hausi A. M¨uller,Supervisor (Department of Computer Science) Dr. Alex I. Thomo, Departamental Member (Department of Computer Science) iii Supervisory Committee Dr. Hausi A. M¨uller,Supervisor (Department of Computer Science) Dr. Alex I. Thomo, Departamental Member (Department of Computer Science) ABSTRACT As software systems have grown in size and complexity, the costs of maintaining such systems increases steadily. In the early 2000's, IBM launched the autonomic com- puting initiative to mitigate this problem by injecting feedback control mechanisms into software systems to enable them to observe their health and self-heal without human intervention and thereby cope with certain changes in their requirements and environments. Self-healing is one of several fundamental challenges addressed and includes software systems that are able to recover from failure conditions. There has been considerable research on software architectures with feedback loops that allow a multi-component system to adjust certain parameters automatically in response to changes in its environment.
    [Show full text]
  • Test-‐Driven Development Step Patterns for Designing Objects
    Test-Driven Development Step Patterns For Designing Objects Dependencies EDUARDO GUERRA, National Institute for Space Research, Brazil JOSEPH YODER, Refactory Inc., USA MAURÍCIO FINAVARO ANICHE, University of São Paulo, Brazil MARCO AURÉLIO GEROSA, University of São Paulo, Brazil Test-driven development (TDD) is a development technique often used to design classes in a software system by creating tests before their actual code. The dependency management and class APIs decisions, that emerge during the practice of TDD, does not "just happen": the way that the tests are created should be used in this process to make decisions and drive the design in the desired direction. This paper introduces four patterns that document the kinds of TDD cycles that can be performed to guide the design in the desired direction. These patterns are part of a pattern language that intends to present recurrent solutions that are used in a TDD process. Categories and Subject Descriptors: D.1.5 [Programming Techniques]: Object-oriented Programming; D.2.11 [Software Architectures]: Patterns General Terms: Test driven development Additional Key Words and Phrases: TDD, softWare design, patterns ACM Reference Format: Guerra, E., Yoder, J., Aniche, M. and Gerosa, M.. 2013. Test-Driven Development Step Patterns For Designing Objects Dependencies. Proceedings of the 20th Conference on Pattern Languages of Programs (PLoP). October 2013, 15 pages. 1. INTRODUCTION Test-driven development (TDD) is a technique in Which the tests are Written before the production code (Beck 2002). By using it, the development occurs in cycles, comprised of the creation of an automated test, an update on the developed softWare to make the test pass, and a code refactoring to improve the solution.
    [Show full text]
  • To Mock Or Not to Mock?
    Delft University of Technology To Mock or Not To Mock? An Empirical Study on Mocking Practices Spadini, Davide; Aniche, Maurício; Bruntink, Magiel; Bacchelli, Alberto DOI 10.1109/MSR.2017.61 Publication date 2017 Document Version Accepted author manuscript Published in Proceedings - 2017 IEEE/ACM 14th International Conference on Mining Software Repositories, MSR 2017 Citation (APA) Spadini, D., Aniche, M., Bruntink, M., & Bacchelli, A. (2017). To Mock or Not To Mock? An Empirical Study on Mocking Practices. In Proceedings - 2017 IEEE/ACM 14th International Conference on Mining Software Repositories, MSR 2017 (pp. 402-412). [7962389] IEEE . https://doi.org/10.1109/MSR.2017.61 Important note To cite this publication, please use the final published version (if applicable). Please check the document version above. Copyright Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons. Takedown policy Please contact us and provide details if you believe this document breaches copyrights. We will remove access to the work immediately and investigate your claim. This work is downloaded from Delft University of Technology. For technical reasons the number of authors shown on this cover page is limited to a maximum of 10. Delft University of Technology Software Engineering Research Group Technical Report Series To Mock or Not To Mock? An Empirical Study
    [Show full text]
  • Private API Access and Functional Mocking in Automated Unit Test Generation
    Private API Access and Functional Mocking in Automated Unit Test Generation Andrea Arcuri Gordon Fraser René Just Westerdals Oslo ACT University of Sheffield University of Massachusetts Oslo, Norway, Sheffield, UK Amherst, MA, USA and SnT, University of Luxembourg Abstract—Not all object oriented code is easily testable: 1 public interface AnInterface { Dependency objects might be difficult or even impossible to 2 boolean isOK(); instantiate, and object-oriented encapsulation makes testing po- 3 } tentially simple code difficult if it cannot easily be accessed. 4 5 public class PAFM { When this happens, then developers can resort to mock objects 6 that simulate the complex dependencies, or circumvent object- 7 public void example(AnInterface x) { oriented encapsulation and access private APIs directly through 8 if(System.getProperty("user.name").equals("root")) { the use of, for example, Java reflection. Can automated unit test 9 checkIfOK(x); 10 } generation benefit from these techniques as well? In this paper 11 } we investigate this question by extending the EvoSuite unit test 12 generation tool with the ability to directly access private APIs 13 private boolean checkIfOK(AnInterface x){ and to create mock objects using the popular Mockito framework. 14 if(x.isOK()){ 15 return true; However, care needs to be taken that this does not impact the 16 } else{ usefulness of the generated tests: For example, a test accessing a 17 return false; private field could later fail if that field is renamed, even if that 18 } renaming is part of a semantics-preserving refactoring. Such a 19 } } failure would not be revealing a true regression bug, but is a 20 false positive, which wastes the developer’s time for investigating and fixing the test.
    [Show full text]
  • Automated Unit Test Generation for Classes with Environment Dependencies
    Automated Unit Test Generation for Classes with Environment Dependencies Andrea Arcuri Gordon Fraser Juan Pablo Galeotti Certus Software V&V Center University of Sheffield Saarland University – Simula Research Laboratory Dep. of Computer Science Computer Science Lysaker, Norway Sheffield, UK Saarbrücken, Germany ABSTRACT 1 public class EnvExample { 2 Automated test generation for object-oriented software typically 3 public boolean checkContent() throws Exception{ consists of producing sequences of calls aiming at high code cov- 4 erage. In practice, the success of this process may be inhibited 5 Scanner console = new Scanner(System.in); when classes interact with their environment, such as the file sys- 6 String fileName = console.nextLine(); 7 console.close(); tem, network, user-interactions, etc. This leads to two major prob- 8 lems: First, code that depends on the environment can sometimes 9 File file = new File(fileName); not be fully covered simply by generating sequences of calls to a 10 if(!file.exists()) 11 return false; class under test, for example when execution of a branch depends 12 on the contents of a file. Second, even if code that is environment- 13 Scanner fromFile = new Scanner(new FileInputStream( dependent can be covered, the resulting tests may be unstable, i.e., file)); 14 String fileContent = fromFile.nextLine(); they would pass when first generated, but then may fail when exe- 15 fromFile.close(); cuted in a different environment. For example, tests on classes that 16 String date = DateFormat.getDateInstance(DateFormat. make use of the system time may have failing assertions if the tests SHORT).format(new Date()); 17 if(fileContent.equals(date)) are executed at a different time than when they were generated.
    [Show full text]
  • Assessing Mock Classes: an Empirical Study
    Assessing Mock Classes: An Empirical Study Gustavo Pereira, Andre Hora ASERG Group, Department of Computer Science (DCC) Federal University of Minas Gerais (UFMG) Belo Horizonte, Brazil fghapereira, [email protected] Abstract—During testing activities, developers frequently SinonJS1 and Jest,2 which is supported by Facebook; Java rely on dependencies (e.g., web services, etc) that make the developers can rely on Mockito3 while Python provides test harder to be implemented. In this scenario, they can use unittest.mock4 in its core library. The other solution to create mock objects to emulate the dependencies’ behavior, which contributes to make the test fast and isolated. In practice, mock classes is by hand, that is, manually creating emulated the emulated dependency can be dynamically created with the dependencies so they can be used in test cases. In this case, support of mocking frameworks or manually hand-coded in developers do not need to rely on any particular mocking mock classes. While the former is well-explored by the research framework since they can directly consume the mock class. literature, the latter has not yet been studied. Assessing mock For example, to facilitate web testing, the Spring web classes would provide the basis to better understand how those mocks are created and consumed by developers and to detect framework includes a number of classes dedicated to mock- 5 novel practices and challenges. In this paper, we provide the ing. Similarly, the Apache Camel integration framework first empirical study to assess mock classes. We analyze 12 provides mocking classes to support distributed and asyn- popular software projects, detect 604 mock classes, and assess chronous testing.6 That is, in those cases, instead of using their content, design, and usage.
    [Show full text]
  • David Keen Object Oriented Programming Mock Objects and Test Driven Design (TDD) the Text of This Essay Is My Own, Except Where
    David Keen Object Oriented Programming Mock Objects and test driven design (TDD) The text of this essay is my own, except where explicitly indicated. I give my permission for this essay to be submitted to the JISC Plagiarism Detection Service. Test every work of intellect or faith And everything that your own hands have wrought William Butler Yeats Mock Objects are a relatively new tool in the object oriented programmer's toolkit. Developed by Tim Mackinnon, Steve Freeman, and Philip Craig and first presented at the conference “eXtreme Programming and Flexible Processes in Software Engineering – XP2000”, Mock Objects are a powerful aid to Unit Testing and Test Driven Development. Many programmers are familiar with unit testing. Basically, this involves writing tests for some or all of the classes and methods in a program. There are a number of unit testing frameworks such as the xUnit family, first designed by Kent Beck for SmallTalk but now extended to more than twenty- five different frameworks for languages such as C++, Perl, Java and PHP. The goal of unit testing is to isolate each method or function and, through the use of an automated testing framework, write tests than can be repeatedly run to verify the correctness of the code. Having complete coverage of your code with unit tests gives you the confidence that any change you make to existing code does not introduce new errors in other parts of your program. Unit testing is an important part of the eXtreme Programming methodology as well as other Agile methodologies such as Scrum. But Test Driven Development is more than just unit testing.
    [Show full text]
  • Unit Testing Services Built on Top of a Legacy System Using Mock Objects and the Adapter Pattern Ketil Jensen Miles IT
    Unit testing services built on top of a legacy system using mock objects and the adapter pattern Ketil Jensen Miles IT Abstract Legacy systems with a growing code base has become an increasing burden in the IT industry the last couple of years. Often these systems has grown to become colossal systems with an unclear architecture and messy interfaces that are difficult to use. At the same time there is an ever-increasing need to integrate more and more IT systems in companies to meet new demands are increasing. As a consequence, exposing functionality from legacy systems as services is becoming common This is of course a good thing since clients then can more easily integrate with these legacy systems. However, one should be careful so that one does not just build yet another layer on top of an already existing pile of rotten code. The challenge The figure shows a simplified view of the architecture for the system that we will look into for the rest of this paper. Our task is to create Service layer services on top of an already existing core layer. This layer has grown into a huge unmaintainabke Core API system over many years and has a messy and DB unclear interface, in short it has all the bad signs of a legacy system which pretty soon will be a Legacy system bottleneck for the organization. The core API consists almost solely of concrete classes and instantiation of some of these classes results in an initialization of nearly all the different DB systems in the chain.
    [Show full text]
  • Chapter 8, Object Design: Design Patterns II
    Chapter 8, Object Design: Design Patterns II Object-Oriented Software EngineeringSoftwareObject-Oriented Using UML, andJava Patterns, Recall: Why reusable Designs? A design… …enables flexibility to change (reusability) …minimizes the introduction of new problems when fixing old ones (maintainability) …allows the delivery of more functionality after an initial delivery (extensibility) …encapsulates software engineering knowledge. Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 3 How can we describe Software Engineering Knowledge? • Software Engineering Knowledge is not only a set of algorithms • It also contains a catalog of patterns describing generic solutions for recurring problems • Not described in a programming language. • Description usually in natural language. A pattern is presented in form of a schema consisting of sections of text and pictures (Drawings, UML diagrams, etc.) Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 4 Design Patterns • Design Patterns are the foundation for all SE patterns • Based on Christopher Alexander‘s patterns • Book by John Vlissedes, Erich Gamma, Ralph Johnson and Richard Helm, also called the Gang of Four • Idea for the book at a BOF "Towards an Architecture Handbook“ (Bruce Anderson at OOPSLA’90) John Vlissedes Erich Gamma Ralph Johnson Richard Helm •* 1961-2005 •* 1961 •* 1955 • University of Melbourne •Stanford •ETH •University of Illinois, •IBM Research, Boston •IBM Watson •Taligent, IBM
    [Show full text]