User stories, acceptance criteria and INVEST for the CAPM
A user story describes a user and why they need the service, and GOV.UK says it must always include the actor, the narrative and the goal. Acceptance criteria are a checklist of outcomes, often written 'it's done when...', that confirm the story meets the user need. INVEST is a checklist for judging a story's quality.
Writing the story
The usual format is: As a... [who is the user?] I need/want/expect to... [what does the user want to do?] So that... [why?]. GOV.UK's example: 'as a UK resident, I want to get my details on the electoral register so that I can vote'.
The goal is the most important part. It shows you are solving the right problem and tells you when the story is done. If you cannot write the goal, reconsider whether the feature is needed.
Stories that would take more than a few weeks are epics; split them into stories that fit within an iteration. All stories go in the backlog, where the product manager orders them by priority until the team is ready to work on them.
Acceptance criteria and tests
Acceptance criteria are a list of outcomes used as a checklist to confirm the service meets the user need, for example 'it's done when the user knows where to send the form'. They can link to supporting evidence such as spreadsheets or diagrams.
Given-When-Then is a template for acceptance tests: given some context, when some action is carried out, then a set of observable consequences should follow.
In XP, the customer specifies the scenarios that acceptance tests check, and a story is not complete until it passes its acceptance tests.
INVEST and the Three Cs
INVEST is a checklist for story quality: Independent, Negotiable (not a contract for features), Valuable, Estimable, Small (fits within an iteration) and Testable.
The Three Cs describe a story's parts: the Card that gives it physical form, the Conversation among customers, users, developers and testers, and the Confirmation that its objectives were reached.
Where the exam catches people
Believing acceptance criteria are a required part of every story: GOV.UK requires actor, narrative and goal, and says you can also include acceptance criteria.
Believing the narrative is the most important part of a story: GOV.UK says the goal is.
Believing a story card is a full specification: the Three Cs treat the card as a token for a conversation, confirmed later.
Believing developers write XP acceptance test scenarios: the customer specifies them.
Believing a story too big for an iteration should just run over: split it into smaller stories.