Functional Requirement
A Functional Requirement specifies what the system should do—the features, behaviors, and business rules the application must support.
Functional requirements answer: “What functionality must the system provide?”
1. Definition
A Functional Requirement specifies what the system should do—the features, behaviors, and business rules the application must support.
Functional requirements answer: “What functionality must the system provide?”
2. Purpose of Functional Requirements
- Define system behavior clearly
- Serve as the basis for design, development, and testing
- Ensure business needs are met
- Enable functional test case creation
3. Characteristics of a Good Functional Requirement
- Clear and unambiguous
- Complete and consistent
- Testable and measurable
- Traceable to business needs
- Independent of implementation
4. Common Formats of Functional Requirements
- Shall statements
- “The system shall allow users to reset passwords.”
- Use cases
- User stories with acceptance criteria
5. Manual Tester’s Role
- Review functional requirements for clarity and testability
- Identify missing scenarios and edge cases
- Derive test scenarios and test cases
- Validate implementation against requirements
- Map requirements in RTM
6. Examples of Functional Requirements
Example 1: Login
- The system shall allow users to log in using valid credentials.
- The system shall display an error message for invalid credentials.
Example 2: Order Processing
- The system shall calculate total price including tax.
- The system shall prevent checkout if items are out of stock.
7. Functional vs Non-Functional Requirements
| Aspect | Functional | Non-Functional |
|---|---|---|
| Focus | What system does | How system performs |
| Examples | Login, Payment | Performance, Security |
| Testing | Functional testing | Non-functional testing |
8. Common Functional Requirement Issues
- Vague wording (“should”, “as required”)
- Missing validation rules
- Unclear error handling
- Implicit assumptions
9. Functional Requirements vs Acceptance Criteria
| Aspect | Functional Requirement | Acceptance Criteria |
|---|---|---|
| Level | Feature-level | Story-level |
| Purpose | Define behavior | Define acceptance |
10. Interview-Ready Answers
Short answer:
Functional requirements define what functionality the system must provide.
Detailed answer:
Functional requirements describe system behaviors and business rules that specify how the system should respond to inputs and actions.
11. Key Takeaway
Functional Requirements are the foundation of manual testing, driving scenarios, test cases, and validation.