🎯 What Are Test Design Techniques?
Test design techniques are structured methods used by QA professionals to create effective and efficient test cases. They help ensure good coverage of requirements, uncover edge cases, and avoid redundant testing.
These techniques are a core part of the ISTQB Foundation Level syllabus, and every QA engineer—manual or automation—should understand them.
🧪 Why Are Test Design Techniques Important?
- Ensure maximum coverage with minimal test cases
- Save time by avoiding unnecessary testing
- Catch defects early in the software lifecycle
- Improve test planning, quality, and traceability
- Align with client and stakeholder expectations
🔹 Types of Test Design Techniques
Test design techniques fall into three main categories:
1. Black-Box Techniques
Based on inputs and outputs, not internal code structure.
Used when you don’t have access to the source code.
Common Black-Box Techniques:
- Equivalence Partitioning
Divide inputs into valid/invalid classes and test one from each. - Boundary Value Analysis
Focus on values at the edge (e.g., min/max, just inside/outside). - Decision Table Testing
Use logical conditions and actions to create a rule-based matrix. - State Transition Testing
Test changes in state based on events (e.g., login > logout > lockout). - Use Case Testing
Validate real-world user scenarios.
2. White-Box Techniques
Based on the internal logic or structure of the application.
Used when you have access to the source code.
Common White-Box Techniques:
- Statement Coverage
Ensure every line of code is executed at least once. - Decision Coverage
Ensure every possible decision (true/false) is tested. - Condition Coverage
Test all individual conditions in a decision.
3. Experience-Based Techniques
Based on the tester’s intuition, domain knowledge, or past experience.
These are useful when requirements are unclear or exploratory testing is needed.
Examples:
- Error Guessing
Based on common bugs or past mistakes. - Exploratory Testing
Simultaneous test design and execution. - Checklist-Based Testing
Use a predefined checklist to ensure coverage.
📊 Quick Comparison Table
| Technique Type | Examples | Best For |
|---|---|---|
| Black-Box | Equivalence, Boundary, Decision | Input validation, business logic |
| White-Box | Statement, Decision, Condition | Code coverage, logic validation |
| Experience-Based | Error Guessing, Exploratory | Unstructured, edge case discovery |
📝 Real-Life Example: ATM Withdrawal
Requirement:
An ATM only allows withdrawals between $20 and $500, in multiples of $10.
Test Design Techniques in Action:
- Equivalence Partitioning:
- Valid: $100
- Invalid: $5, $700
- Boundary Value Analysis:
- Test: $19, $20, $500, $501
- Decision Table:
- Create a matrix with conditions (e.g., balance > amount, card valid) and outcomes.
- State Transition:
- Insert card → Enter PIN → Select amount → Withdraw → Eject card
✅ Best Practices for Applying Test Design Techniques
- Read and understand the requirements thoroughly.
- Choose multiple techniques for thorough coverage.
- Document which technique you’re using for traceability.
- Use boundary values even when doing equivalence testing.
- Practice combining methods (e.g., Equivalence + Boundary).
📚 Summary
| Key Takeaway |
|---|
| Test design techniques help you create fewer, smarter, and more effective test cases. |
They’re a must-have in every QA playbook, whether you’re preparing for ISTQB, improving your manual testing, or starting with automation.
