Error Guessing

Error Guessing is an experience-based test design technique where testers anticipate possible defects based on their knowledge, intuition, and past experience.

Error guessing answers: “Where is the system likely to fail?”

1. Definition

Error Guessing is an experience-based test design technique where testers anticipate possible defects based on their knowledge, intuition, and past experience.

Error guessing answers: “Where is the system likely to fail?”

2. Purpose of Error Guessing

• Identify defects not covered by formal techniques
• Leverage tester experience
• Detect real-world and edge-case issues
• Complement structured test cases

3. Basis for Error Guessing

Testers rely on:

• Past defect history
• Domain knowledge
• Common developer mistakes
• Similar application behavior

4. Typical Error Guessing Scenarios

• Blank or null inputs
• Special characters
• Boundary violations
• Unexpected user actions
• Repeated actions (double-click, refresh)

5. Manual Tester’s Role

• Apply intuition and creativity
• Explore high-risk areas
• Think like a careless or malicious user
• Log unexpected failures

6. Error Guessing vs Formal Techniques

7. Real-Time Example

While testing a file upload:

• Upload unsupported file type
• Upload large file
• Upload file with special characters in name

8. Common Defects Found

• Application crashes
• Unhandled exceptions
• Validation bypass
• Poor error handling

9. Common Mistakes

• Treating error guessing as random testing
• Over-reliance without documentation
• Ignoring repeatability

10. Interview-Ready Answers

Short answer:

Error guessing is a test design technique based on tester experience to anticipate where defects might occur.

Detailed answer:

Error guessing leverages prior knowledge, intuition, and experience to identify likely defect-prone areas beyond structured test cases.

11. Key Takeaway

Error Guessing is powerful when guided by experience and insight, not randomness.