How to Derive Effective Test Cases? The Ultimate ISTQB-Based Guide

Deriving effective test cases is one of the most valuable skills in the software testing world. But it’s not about writing random tests or checking the obvious. The key is to apply formal and structured techniques that ensure product quality, minimize risks, and optimize testing effort. In this post, you'll learn how to do it professionally, aligned with the ISTQB Foundation Level (CTFL) certification.

📌 What does “derive” mean in testing?

To “derive” test cases means transforming test bases (requirements, models, business rules, etc.) into executable scenarios or scripts. This is part of the test design phase in the testing process.

🧠 ISTQB test design techniques

The ISTQB groups test design techniques into three main categories:

1. Specification-based techniques (Black-box)
2. Structure-based techniques (White-box)
3. Experience-based techniques

1. Specification-based techniques:

These focus on what the system should do. Examples:

• Equivalence Partitioning
• Boundary Value Analysis
• Decision Tables
• State Transition Testing

2. Structure-based techniques:

These focus on the internal structure of the code:

• Statement and decision coverage
• Multiple condition testing

3. Experience-based techniques:

These rely on the tester’s intuition and past experience:

• Exploratory testing
• Common error checklists
• Risk-based attacks

💡 Example: ATM Machine

"The ATM allows withdrawals between 20 and 2000, in multiples of 10."

Using test design techniques:

• Equivalence Partitioning:
  • Valid: 100, 500
  • Invalid: 5, 2500
• Boundary Value Analysis:
  • Lower boundary: 20, 10 (invalid)
  • Upper boundary: 2000, 2010 (invalid)

🔁 Best Practices

• Make sure your test basis is well understood.
• Combine multiple techniques for better coverage.
• Prioritize based on risk.
• Document the rationale behind each test.
• Use visual aids (flowcharts, tables).

✅ Conclusion

Deriving test cases is a disciplined practice that blends analytical skills and structured methods. It’s essential for anyone pursuing a professional testing career or preparing for ISTQB certification.