Three-Point Estimation for Test Execution Time
1. Introduction
In testing projects, estimating effort accurately is important for planning, scheduling, and risk management.
The ISTQB Foundation Level syllabus introduces three-point estimation as a technique that accounts for uncertainty by considering optimistic, pessimistic, and most likely scenarios.
테스트 프로젝트에서는 테스트 수행 시간 추정이 매우 중요합니다.
ISTQB에서는 불확실성을 반영하기 위해 3점 추정(Three-point estimation) 기법을 사용합니다.
2. Practice Question
❓ Question
The team wants to estimate the time needed for one tester to execute four test cases for a software component.
The following effort estimates are available for executing a single test case:
- Best-case scenario: 1 hour
- Worst-case scenario: 8 hours
- Most likely scenario: 3 hours
Using the three-point estimation technique, what is the final estimate of the time needed to execute all four test cases?
- a) 14 hours
- b) 3.5 hours
- c) 16 hours
- d) 12 hours
✅ Correct Answer: a)
3. Explanation
Step 1: Apply the three-point estimation formula
The three-point (PERT) estimation formula is:
E = (a + 4m + b) / 6
Where:
- a = optimistic (best-case) estimate
- m = most likely estimate
- b = pessimistic (worst-case) estimate
For one test case:
- a = 1 hour
- m = 3 hours
- b = 8 hours
Calculation:
E = (1 + 4×3 + 8) / 6 = (1 + 12 + 8) / 6 = 21 / 6 = 3.5 hours
테스트 케이스 1개의 실행 시간에 대한 3점 추정 결과는 3.5시간입니다.
Step 2: Calculate total effort for four test cases
Each test case takes an estimated 3.5 hours.
For 4 test cases:
3.5 × 4 = 14 hours
따라서 테스트 케이스 4개를 실행하는 데 필요한 총 예상 시간은 14시간입니다.
✔ a) 14 hours — Correct
This option correctly:
- Applies the three-point estimation formula
- Uses the estimate for one test case
- Multiplies it by the total number of test cases
Why the other options are incorrect
❌ b) 3.5 hours
This value represents the estimate for one test case only, not for all four test cases.
❌ c) 16 hours
This value is not derived from the three-point estimation formula and does not match any valid calculation.
❌ d) 12 hours
This is calculated using only the most likely estimate (3 hours × 4) and ignores uncertainty.
4. Summary Table
| Item | Calculation | Result | 설명 |
|---|---|---|---|
| Single test case | (1 + 4×3 + 8) / 6 | 3.5 hours | 3점 추정 |
| Four test cases | 3.5 × 4 | 14 hours | 총 실행 시간 |
5. Final Takeaway
For the ISTQB exam, remember:
Three-point estimation calculates a weighted average using optimistic, most likely, and pessimistic values, and the total effort is obtained by multiplying by the number of test cases.
시험 대비 핵심 문장입니다.
3점 추정은 낙관·가능·비관 값을 가중 평균으로 계산하며, 전체 테스트 시간은 테스트 케이스 수만큼 곱해서 산정한다.
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