/qa-manual-istqb

Test Design Techniques (ISTQB Foundation Level)

Part of the qa-manual-istqb skill. See SKILL.md for full context.

Test design techniques transform the test basis into test conditions and test cases. Choose techniques based on the type of testing and risk level.

Technique Categories

Black-Box Techniques

1. Equivalence Partitioning (EP)

Use when: Inputs can be grouped into classes that should behave the same way.

How it works:

1. Identify input parameters and their valid/invalid ranges
2. Divide each into partitions (groups of equivalent values)
3. Select one representative value per partition
4. Each partition needs at least one test case

Example: Age field (valid range: 18-65)

Test cases: 3 tests (one per partition)

2. Boundary Value Analysis (BVA)

Use when: Defects often occur at boundaries of ranges/limits.

How it works:

1. Identify boundaries from equivalence partitions
2. Test values at, just below, and just above each boundary
3. Two-value BVA: boundary and one neighbor
4. Three-value BVA: boundary and both neighbors

Example: Age field (valid range: 18-65)

Test values (three-value): 17, 18, 19, 64, 65, 66 (6 tests)

Combining EP + BVA:

• EP confirms partitions work
• BVA tests transitions between partitions

3. Decision Table Testing

Use when: Business rules combine multiple conditions to determine actions.

How it works:

1. List all conditions (inputs)
2. List all actions (outputs)
3. Create columns for all condition combinations
4. Mark which actions apply for each combination
5. Eliminate impossible or redundant combinations
6. One test per rule (column)

Example: Discount rules

Test cases: 4 tests (one per rule)

Simplified decision tables: Collapse rows when a condition doesn't affect the action.

4. State Transition Testing

Use when: System behavior depends on state/history (orders, sessions, workflows).

How it works:

1. Identify all states
2. Identify all transitions (events that cause state changes)
3. Draw state diagram
4. Test valid transitions (happy paths)
5. Test invalid transitions (should be rejected)
6. Test transition sequences (0-switch, 1-switch, etc.)

Example: Order status

[New] --confirm--> [Confirmed] --ship--> [Shipped] --deliver--> [Delivered]
                        |                     |
                        +--cancel--> [Cancelled] <--cancel--+

State transition table:

Coverage levels:

• All states: Each state visited at least once
• All transitions (0-switch): Each transition exercised
• 1-switch: Every pair of adjacent transitions

5. Use Case / Scenario Testing

Use when: Testing end-to-end user journeys and workflows.

How it works:

1. Identify use cases from requirements
2. Define main success scenario (happy path)
3. Define alternate flows (variations)
4. Define exception flows (error handling)
5. Create tests for each flow

Example: Online purchase

Coverage Criteria Summary

Selecting Techniques

Combining Techniques

For thorough coverage, combine techniques:

1. EP + BVA for input fields (partitions + boundaries)
2. Decision tables for rule combinations
3. State transitions for status/workflow
4. Use cases for end-to-end validation
5. Exploratory for edge cases and discovery

Example: Testing a login form