SOFTWARE ENGINEERING (CO3001) Agile Software Development WEEK 3 Jan 2018 Chapter 3. Agile Software Development 2 Topics covered • Agile methods • Agile development techniques • Agile project management • Scaling agile methods Jan 2018 Chapter 3. Agile Software Development 3 Rapid software development • Rapid development and delivery is now often the most important requirement for software systems • Businesses operate in a fast-changing requirement • => practically impossible to have stable software requirements • Software has to evolve quickly to reflect changing business needs. • Plan-driven development (waterfall, incremental dev.) is essential for some types of system but does not meet these business needs.
Agile Software Development 4 Ø emerged in the late 1990s Agile development Ø aim to radically reduce the delivery time for working software systems • Program specification, design and implementation are inter-leaved • The system = a series of versions / increments • Stakeholders involved in version specification and evaluation • Frequent delivery of new versions for evaluation • Minimal documentation – focus on working code • Extensive tool support (e. automated testing tools) used to support development. Agile Software Development 5 Plan-driven and agile development Plan-based development i.: waterfall model, incremental development Requirements Requirements Design and engineering specification implementation Requirements change requests Agile development Requirements Design and engineering implementation Jan 2018 Chapter 3. Agile Software Development 6 AGILE METHODS Jan 2018 Chapter 3.
Agile Software Development 7 Agile methods • Agile methods: • Focus on the code rather than the design • Are based on an iterative approach to software development • Are intended to deliver working software quickly and evolve this quickly to meet changing requirements. • Aims: • to reduce overheads in the software process (e. by limiting documentation) • to respond quickly to changing requirements without excessive rework. Agile Software Development 8 The principles of agile methods Principle Description Customer involvement Customers should be closely involved throughout the development process.
Their role is provide and prioritize new system requirements and to evaluate the iterations of the system. Incremental delivery The software is developed in increments with the customer specifying the requirements to be included in each increment. People, not process The skills of the development team should be recognized and exploited. Team members should be left to develop their own ways of working without prescriptive processes.
Embrace change Expect the system requirements to change and so design the system to accommodate these changes. Maintain simplicity Focus on simplicity in both the software being developed and in the development process. Wherever possible, actively work to eliminate complexity from the system. Agile Software Development 9 Agile method applicability • For a small or medium-sized product for sale.
• Virtually all software products and apps are now developed using an agile approach • Clear commitment from the customer to become involved • in the development process • and where there are few external rules and regulations that affect the software. Agile Software Development 10 AGILE DEVELOPMENT TECHNIQUES Jan 2018 Chapter 3. Agile Software Development 11 Extreme programming late 1990s • Extreme Programming (XP) takes an ‘extreme’ approach to iterative development. • New versions may be built several times per day; • Increments are delivered to customers every 2 weeks; • All tests must be run for every build and the build is only accepted if tests run successfully.
Select user Break down stories for this Plan release stories to tasks release The XP release cycle Evaluate Release Develop/integrate/ system software test software Jan 2018 Chapter 3. Agile Software Development 12 Extreme programming practices (a) Principle or practice Description Incremental planning Requirements are recorded on story cards and the stories to be included in a release are determined by the time available and their relative priority. The developers break these stories into development ‘Tasks’. Small releases The minimal useful set of functionality that provides business value is developed first.
Releases of the system are frequent and incrementally add functionality to the first release. Simple design Enough design is carried out to meet the current requirements and no more. Test-first development An automated unit test framework is used to write tests for a new piece of functionality before that functionality itself is implemented. Refactoring All developers are expected to refactor the code continuously as soon as possible code improvements are found.
This keeps the code simple and maintainable. Agile Software Development 13 Extreme programming practices (b) Pair programming Developers work in pairs, checking each other’s work and providing the support to always do a good job. Collective ownership The pairs of developers work on all areas of the system, so that no islands of expertise develop and all the developers take responsibility for all of the code. Anyone can change anything.
Continuous integration As soon as the work on a task is complete, it is integrated into the whole system. After any such integration, all the unit tests in the system must pass. Sustainable pace Large amounts of overtime are not considered acceptable as the net effect is often to reduce code quality and medium term productivity On-site customer A representative of the end-user of the system (the customer) should be available full time for the use of the XP team. In an extreme programming process, the customer is a member of the development team and is responsible for bringing system requirements to the team for implementation.
Agile Software Development 14 XP and agile principles • Incremental development • supported through small, frequent system releases. • Customer involvement • means full-time customer engagement with the team. • People not process • through pair programming, collective ownership and a process that avoids long working hours. • Change supported • through regular system releases.
• Maintaining simplicity • through constant refactoring of code. Agile Software Development 15 Influential XP practices • Extreme programming has a technical focus and is not easy to integrate with management practice in most organizations. • Consequently, while agile development uses practices from XP, the method as originally defined is not widely used. • Key practices • User stories for specification • Refactoring • Test-first development • Pair programming Jan 2018 Chapter 3.
Agile Software Development 16 User stories for requirements • In XP, a customer or user is part of the XP team and is responsible for making decisions on requirements. • User requirements are expressed as user stories or scenarios. • These are written on cards and the development team break them down into implementation tasks. These tasks are the basis of schedule and cost estimates.
• The customer chooses the stories for inclusion in the next release based on their priorities and the schedule estimates. Agile Software Development 17 A ‘prescribing medication’ story Jan 2018 Chapter 3. Agile Software Development 18 Examples of task cards for prescribing medication Task 1: Change dose of prescribed drug Task 2: Formulary selection Task 3: Dose checking Dose checking is a safety precaution to check that the doctor has not prescribed a dangerously small or large dose. Using the formulary id for the generic drug name, lookup the formulary and retrieve the recommended maximum and minimum dose.
Check the prescribed dose against the minimum and maximum. If outside the range, issue an error message saying that the dose is too high or too low. If within the range, enable the ‘Confirm’ button. Agile Software Development 19 Refactoring • Conventional wisdom: design for change, anticipating changes => reduce cost later in life cycle • XP: constant code improvement (refactoring) to make changes easier when they have to be implemented.
• Make possible software improvements • even where there is no immediate need for them. • Refactoring advantages: • Improves the understandability of the software => reduces the need for documentation. • Code is well-structured and clear => changes are easier to make • Disadvantages: • some changes requires architecture refactoring => expensive. Agile Software Development 20 Examples of refactoring • Re-organization of a class hierarchy to remove duplicate code.
• Tidying up and renaming attributes and methods to make them easier to understand. • The replacement of inline code with calls to methods that have been included in a program library. Agile Software Development 21 Test-first development • Testing is central to XP and XP has developed an approach where the program is tested after every change has been made. • XP testing features: • Test-first development.
• Incremental test development from scenarios. • User involvement in test development and validation. • Automated test harnesses are used to run all component tests each time that a new release is built. Agile Software Development 22 Test-driven development • Writing tests before code clarifies the requirements to be implemented.
• Tests are written as programs rather than data so that they can be executed automatically. The test includes a check that it has executed correctly. • Usually relies on a testing framework such as JUnit. • All previous and new tests are run automatically when new functionality is added, thus checking that the new functionality has not introduced errors.
Agile Software Development 23 Customer involvement in testing • The role of the customer in the testing process is to help develop acceptance tests for the stories that are to be implemented in the next release of the system. • The customer who is part of the team writes tests as development proceeds. All new code is therefore validated to ensure that it is what the customer needs. • However, people adopting the customer role have limited time available and so cannot work full-time with the development team.
They may feel that providing the requirements was enough of a contribution and so may be reluctant to get involved in the testing process. Agile Software Development 24 Test case description for dose checking Test 4: Dose checking Input: 1. A number in mg representing a single dose of the drug. A number representing the number of single doses per day.
Test for inputs where the single dose is correct but the frequency is too high. Test for inputs where the single dose is too high and too low. Test for inputs where the single dose * frequency is too high and too low. Test for inputs where single dose * frequency is in the permitted range.
Output: OK or error message indicating that the dose is outside the safe range. Agile Software Development 25 Test automation • Test automation means that tests are written as executable components before the task is implemented • These testing components should be stand-alone, should simulate the submission of input to be tested and should check that the result meets the output specification. An automated test framework (e. JUnit) is a system that makes it easy to write executable tests and submit a set of tests for execution.
• As testing is automated, there is always a set of tests that can be quickly and easily executed • Whenever any functionality is added to the system, the tests can be run and problems that the new code has introduced can be caught immediately. Agile Software Development 26 Problems with test-first development • Programmers prefer programming to testing and sometimes they take short cuts when writing tests. For example, they may write incomplete tests that do not check for all possible exceptions that may occur. • Some tests can be very difficult to write incrementally.
For example, in a complex user interface, it is often difficult to write unit tests for the code that implements the ‘display logic’ and workflow between screens. • It difficult to judge the completeness of a set of tests. Although you may have a lot of system tests, your test set may not provide complete coverage. Agile Software Development 27 Pair programming Jan 2018 Chapter 3.
Agile Software Development 28 Pair programming • Working in pairs, developing code together. • Serves as an informal review process • each line of code is looked at by more than 1 person.