Decision Table Coverage (Exam D – Question 22)
1. Introduction
In the ISTQB Foundation Level exam, decision table testing is used to design test cases from business rules that depend on combinations of conditions.
A common goal is to improve decision table coverage by ensuring that each rule (each column) is covered by at least one test case.
ISTQB에서 결정 테이블 테스트(Decision Table Testing)는 조건 조합에 따라 결과가 달라지는 비즈니스 규칙을 테스트할 때 사용합니다.
커버리지를 높이려면 가능한 한 많은 규칙(컬럼)을 테스트 케이스로 커버해야 합니다.
2. Practice Question
❓ Question
You are designing test cases based on the following decision table:
| Rule | R1 | R2 | R3 | R4 | R5 | R6 | R7 |
|---|---|---|---|---|---|---|---|
| C1: Age | 0-18 | 19-65 | 19-65 | >65 | 0-18 | 19-65 | >65 |
| C2: Experience | - | 0-4 | >4 | - | - | - | - |
| C3: Registered? | NO | NO | NO | NO | YES | YES | YES |
| Category | A | A | B | B | B | D | C |
So far you have designed:
- TC1: 19-year-old, unregistered man with no experience → expected: category A
- TC2: 65-year-old, unregistered woman with 5 years of experience → expected: category B
- TC3: 66-year-old, registered man with no experience → expected: category C
- TC4: 65-year-old, registered woman with 4 years of experience → expected: category D
Which test case, when added, will increase the decision table coverage?
- a) 66-year-old, unregistered man with no experience → expected: category B
- b) 55-year-old, unregistered woman with 2 years of experience → expected: category A
- c) 19-year-old, registered woman with 5 years of experience → expected: category D
- d) No additional test case can increase the already achieved decision table coverage
✅ Correct Answer: a)
3. Explanation
Step 1: Identify which rules are already covered
Match each existing test case to a rule (column):
- TC1 (19, unregistered, 0 experience) → matches R2 → Category A
- TC2 (65, unregistered, 5 years experience) → matches R3 → Category B
- TC3 (66, registered, no experience) → matches R7 → Category C
- TC4 (65, registered, 4 years experience) → matches R6 → Category D
So far, rules covered: R2, R3, R6, R7. Uncovered rules: R1, R4, R5.
현재 테스트 케이스는 R2, R3, R6, R7만 커버합니다. 따라서 아직 커버되지 않은 규칙은 R1, R4, R5입니다.
✔ a) 66-year-old, unregistered, no experience → R4 — Correct
For option a:
- Age 66 → >65
- Registered? → NO
- Experience → “-” (ignored for R4)
This matches R4, which is currently uncovered. Therefore, adding option a increases decision table coverage.
선택지 a는 “나이 >65 + 미등록” 조건으로 R4에 해당하며, R4는 기존에 커버되지 않았으므로 커버리지가 증가합니다.
Why the other options do not increase coverage
❌ b) 55-year-old, unregistered, 2 years experience → R2
Age 19–65 + unregistered + experience 0–4 matches R2, already covered by TC1.
❌ c) 19-year-old, registered, 5 years experience → R6
Age 19–65 + registered matches R6 (experience is “-”), already covered by TC4.
❌ d) No additional test case can increase coverage
This is false because only 4 out of 7 rules are covered. Coverage can be increased by adding test cases that match R1, R4, or R5.
b와 c는 이미 커버된 규칙(R2, R6)에 해당하며, d는 아직 미커버 규칙(R1, R4, R5)이 있으므로 틀립니다.
4. Summary Table
| Candidate | Matched Rule | Already Covered? | Coverage Increases? | 결론 |
|---|---|---|---|---|
| a | R4 | ✖ No | ✔ Yes | 정답 |
| b | R2 | ✔ Yes | ✖ No | 중복 |
| c | R6 | ✔ Yes | ✖ No | 중복 |
| d | - | - | ✖ No | 오답 |
5. Final Takeaway
For the ISTQB exam, remember:
Decision table coverage increases when your new test case covers an uncovered rule (column). Here, option a covers R4, which is not yet covered.
시험 대비 핵심 문장입니다.
결정 테이블 커버리지는 새로운 테스트 케이스가 미커버 규칙(컬럼)을 커버할 때 증가한다. 이 문제에서는 a가 R4를 새로 커버하므로 정답이다.
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