Test Estimation Models: PERT, Use-Case Point, WBS

Overview

Test estimation is the process of predicting the time and effort required to complete testing activities. Accurate estimation helps with:

• Resource allocation
• Timeline planning
• Budget forecasting
• Stakeholder communication

There are multiple techniques available, but three commonly used estimation models are:

1. PERT (Program Evaluation and Review Technique)
2. Use-Case Point (UCP) Estimation
3. Work Breakdown Structure (WBS)

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1. PERT Estimation

What It Is:

PERT is a time-based estimation technique that uses three-point estimates to calculate the expected effort.

Formula:

Estimated Time = (Optimistic + 4 × Most Likely + Pessimistic) / 6

Parameters:

• Optimistic (O): Best-case scenario
• Most Likely (M): Most realistic scenario
• Pessimistic (P): Worst-case scenario

Example:

Task	O (hrs)	M (hrs)	P (hrs)	Estimated Time
Test Login	2	4	8	(2+4×4+8)/6 = 4.67 hrs
Test Checkout	5	6	9	(5+4×6+9)/6 = 6.33 hrs

Use Cases:

• When there's uncertainty or lack of historical data
• Ideal for early-stage planning

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2. Use-Case Point (UCP) Estimation

What It Is:

UCP is based on use-case analysis and considers the complexity of:

• Use cases
• Actors (users/systems)
• Technical and environmental factors

Steps:

1. Classify Actors (Simple = 1, Average = 2, Complex = 3)
2. Classify Use Cases (Simple = 5, Average = 10, Complex = 15)
3. Calculate Unadjusted Use Case Points (UUCP)
4. Apply Technical & Environmental Factor weights
5. Final UCP × Productivity Factor = Effort Estimate

Example:

Actors:

• 1 Simple actor (UI) → 1
• 2 Complex actors (external system) → 6
  Total Actor Points = 7

Use Cases:

• 1 Simple UC → 5
• 2 Average UCs → 20
  Total Use Case Points = 25

UUCP = 7 (actors) + 25 (UCs) = 32

Assume adjustment factor = 1.2, productivity = 20 person-hours/UCP

Estimated Effort = 32 × 1.2 × 20 = 768 hours

Use Cases:

• When system requirements are described in use cases
• Common in Agile and UML-driven environments

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3. Work Breakdown Structure (WBS)

What It Is:

WBS involves breaking the testing project into smaller, manageable components and estimating effort for each.

Steps:

1. Identify major testing activities (e.g., test planning, case design, execution, bug reporting)
2. Break each activity into subtasks
3. Estimate effort for each task
4. Sum total for overall estimate

Example:

Activity	Sub-Task	Est. Time (hrs)
Test Planning	Write test strategy	5
Test Design	Design test cases	15
	Review test cases	5
Test Execution	Run regression tests	20
	Log bugs	10
Reporting	Daily status reports	3
Total		58 hrs

Use Cases:

• When scope and deliverables are well-defined
• Helps in task tracking and resource allocation

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Comparison Table

Model	Best For	Key Advantage	Limitation
PERT	Early-stage, uncertain estimates	Incorporates best/worst scenarios	Subjective estimation
UCP	Use-case-driven requirements	Quantitative and scalable	Requires detailed use cases
WBS	Mature projects with known scope	Granular and manageable planning	Can be time-consuming to prepare

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Summary

Choosing the right estimation model depends on your project maturity, requirement clarity, and team experience:

• Use PERT when uncertainty is high
• Use UCP when use cases are well-documented
• Use WBS when tasks can be clearly broken down

“A good estimate is not just a number—it’s a reflection of how well you understand the project.”

Combine these techniques or adapt them for hybrid approaches to suit your team's QA planning process.