Chapter 3: Agile Software Development
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
Influential XP key practices
- User stories for specification - Refactoring - Test-first development - Pair programming
XP and agile principles
-Incremental development is 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.
Scrum (people = process)
"A daily meeting of the Scrum team" that reviews progress and prioritizes work to be done that day. Ideally, this should "be a short face-to-face meeting that includes the whole team"
Development team (small)
"A self-organizing group of software developers, which should be no more than 7 people". They are responsible for developing the software and other essential project documents
Teamwork in Scrum
"The whole team attends short daily meetings (Scrums)" where all team members share information, describe their progress since the last meeting, problems that have arisen and what is planned for the following day
Agile methods
- "Focus on the code" rather than the design - Are based on an "iterative" approach to software quickly and evolve this quickly to meet changing requirements - The aim of agile methods is to reduce overheads in the software process (e.g. by "limiting documentation") and to be able to respond quickly to changing requirements without excessive rework
Agile manifesto
- "Individuals and interactions" over processes and tools - "Working software" over comprehensive documentation - "Customer collaboration" over contract negotiation - "Responding to change" over following a plan
Sprint (short)
A development iteration. Sprints are usually 2 - 4 weeks long
Agile development
- "Program specification, design and implementation are inter-leaved" and the outputs from the development process are decided through a process of "negotiated" during the software development process - The system is developed as a series of versions or increments "with stakeholders involved" in version specification and evaluation - "Frequent delivery of new versions for evaluation" - Extensive tool support (e.g. "automated testing tools with golden test suite") used to support development - Minimal documentation - focus on "working code"
Scaling out and scaling up
- "Scaling up" is concerned with using agile methods for developing "large software systems" that cannot be developed by a small team - "Scaling out" is concerned with how agile methods can be introduced across a "large organization" with many years of software development experience
The Scrum sprint cycle
- "Sprints are fixed length", normally 2 - 4 weeks - The starting point for planning is the "product backlog", which is the list of work to be done on the project - The "selection phase involves all of the project team" who work with the customer to select the features and functionality from the product backlog to be developed during the sprint - During this stage the team is "isolated from the customer and the organization", with all communications channeled through the so-called 'Scrum master' (official single point of "external" contact) - "The role of the Scrum master is to protect the development team from external distractions"
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 - It proposes "constant code improvement (refactoring)" to make changes easier when they have to be implemented - "This improves the understandability of the software and so reduces the need for documentation" - Some changes requires "architecture refactoring and this is much more expensive"
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 - "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
Pair programming
- Developers work in pairs, checking each other's work and providing the support to always do a good job - This helps develop "common ownership of code" and spreads knowledge across the team - It serves as an "informal review" process as each line of code is looked at by more than 1 person - It encourages "refactoring" as the whole team can benefit from improving the system code - Pairs are created dynamically so that all team members work with each other during the development process
Influential XP practices
- Extreme programming has a technical focus and is not easy to integrate with management practice
Agile methods for large systems ("usually not the most suitable approach")
- Large system are usually collections of separate, communicating systems, where separating teams develop each system. Frequently, these teams are working in different places, sometimes in different time zones - Large systems are 'brownfield systems', that is they include and interact with a number of existing systems. Many of the system requirements are concerned with this interaction and so don't really lend themselves to flexibility and incremental development - Where several systems are integrated to create a system, a significant fraction of the development is concerned with system configuration with system configuration rather than original code development
Agile and plan-driven method
- Most projects include elements of plan-driven and agile processes. Deciding on the balance depends on: - Is it important to have a very detailed specification and design before moving to implementation? If so, you probably need to use a plan-driven approach - Is an incremental delivery strategy, where you deliver the software to customers and get rapid feedback from them, realistic? If so, consider using agile methods - How large is the system that is being developed? Agile methods are most effective when the system can be developed with a small co-located team who can communicate informally. This may not be possible for large systems that require larger development teams so a plan-driven approach may have to be used
Contractual issues
- Most software contracts for custom systems are based around a specification, which sets out what has to be implemented by the system developer for the system customer - However, this precludes interleaves specification and development as is the norm in agile development - A contract that pays for developer time rather than functionality is required - However, this is seen as a high risk by many legal departments because what has to be delivered cannot be guaranteed
Examples of refactoring
- Re-organizing 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
Scrum
- Scrum is an agile method that focuses on managing iterative development rather than specific agile practices - There are "three phases" in Scrum - The initial phases is an "outline planning phase" where you establish the general "objectives" for the project and design the software "architecture" - This is followed by "a series of sprint cycles, where each cycle develops an increment of the system" - The project "closure phase" wraps up the project, completes required documentation such as system help frames and user manuals and assesses the lessons learned from the project
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.g. Junit) is a system that makes it easy to write executable tests and submit tests and submit a set of tests for executions - 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
Practical problems with agile methods
- The informality of agile development is "incompatible with the legal approach to contract definition that is commonly used in large companies" - Agile methods are designed for "small co-located teams" yet much software development now involves worldwide distributed teams
Agile project management
- The principle responsibility of software project managers is to manage the project so that the software is delivered "on time and within the planned budget" for the project - Agile project management requires a different approach, which is adapted to "incremental development" and the practices used in agile methods
User stories for 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
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
Velocity (quick and frequent is better)
An estimate of how much product backlog effort that a team can cover a single sprint. Understanding a team's velocity helps them estimate what can be covered in a sprint and provides a basis for measuring improving performance
Product owner
An individual (or possibly a small group) whose job is to identify product features or requirements, prioritize these for development and continuously review the product backlog to ensure that the project continues to meet critical business needs. The Product Owner can be a customer but might also be a product manager in a software company or other stakeholder representative
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
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
Scrum terminology
Development team (small), potentially shippable product increment, product backlog (similar to story card), product owner
Bad Code Smells (Need Refactoring)
Duplicated code, long code, do-it-by-others code, large class, and switch statements
Simple design
Enough design is carried out to meet the current requirements and no more
Embrace change
Expect the system requirements to change and so design the system to accommodate these changes
Extreme Programming Practices
Incremental planning, small releases, simple design, test-first development, refactoring, pair programming, collective ownership (rotating ownership too), continuous integration, sustainable pace, and on site customer
Problems with test-first developments (Write code and test in different times)
It's 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 maintenance
Key problems are: - Lack of product documentation (use architecture specification as the focal documentation) - Keeping customers involved in the development process - Maintaining the continuity of the developmental team
Sustainable pace
Large amounts of overtime are not considered acceptable as the net effect is often to reduce code quality and medium term productivity
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
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
Customer involvement, incremental delivery, people not process, embrace change, and maintain simplicity
The Principles of agile methods
Collective ownership (rotating ownership too)
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
People no 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
Potentially shippable product increment
The software increment that is delivered from a sprint. The idea is that this should be 'potentially shippable' which means that it is in a finished state and no further work, such as testing, is needed to incorporate it into the final product. In practice, this is not always achievable
Incremental delivery
The software is developed in increments with the customer specifying the requirements to be included in each increment
Product Backlog (similar to story card)
This is a list of 'to do' items which the Scrum team must tackle. They may be feature definitions for the software, software requirements, user stories or descriptions of supplementary tasks that are needed, such as architecture definition or user documentation
Agile development methods
emerged in the late 1990s whose aim was to "radically reduce the delivery time for working software systems"
ScrumMaster
is responsible for maintaining the Scrum process and the overall health of the team. "He or she is responsible for interfacing with the rest of the company" and for "ensuring that the Scrum team is not diverted by outside interference"
Agile methods and software maintenance
• Most organizations spend more on maintaining existing software than they do on new software development. So, if agile methods are to be successful, they have to support maintenance as well as original development. • Two key issues: - "Are systems that are developed using an agile approach maintainable, given the emphasis in the development process of minimizing formal documentation?" - Can agile methods be used effectively for evolving a system in response to customer change requests? • "Problems may arise if original development team cannot be maintained".
Rapid software development
• Rapid development and delivery is now often the most important requirement for software systems - Businesses operate in a fast -changing requirement and it is practically impossible to produce a set of stable software requirements - Software has to evolve quickly to reflect changing business needs.