Boundary Testing in Practice

Learning Objectives

By the end of this lesson you will be able to:

Design a complete boundary test suite for a multi-field form
Identify and test implicit boundaries in real systems
Document boundary test results systematically

From Theory to Test Cases

Boundary Value Analysis is only useful when you can execute it systematically on a real specification. In this lesson we work through a complete, realistic example.

Scenario: An online ticket booking system. Users can book 1–10 tickets per order, and each ticket costs $5–$500. The system also applies a 10% discount for orders of 5 or more tickets.

Step 1: Identify All Inputs and Their Boundaries

Input	Valid Range	Lower Boundary	Upper Boundary
Ticket quantity	1–10	1 (min valid)	10 (max valid)
Ticket price	$5–$500	$5 (min valid)	$500 (max valid)

Step 2: Apply Two-Point BVA

Quantity:

0 (invalid), 1 (valid), 10 (valid), 11 (invalid)

Price:

$4 (invalid), $5 (valid), $500 (valid), $501 (invalid)

Step 3: Don't Forget the Business Rule Boundary

The discount triggers at quantity 5. This is a boundary too:

4 tickets: no discount expected
5 tickets: 10% discount expected
The boundary at 5 is as important as the min/max boundaries

Extended test set:

4 tickets, $100 → total $400 (no discount)
5 tickets, $100 → total $450 (10% off → $450)

The Trap: Ignoring Calculated Boundaries

A common mistake is testing only the input fields themselves and forgetting that calculations introduce their own boundaries. In the ticket example:

10 tickets at $500 each → $5,000 total → is that within the Int32 range? Yes.
But what about a system that accumulates daily orders? 1,000 orders × $5,000 = $5,000,000 — still fine for Int32 (max 2.1B).
1,000,000 orders? Now we're at $5 billion — Int32 overflow territory.

Pro Tip: When you see a calculated output field, ask: "What data type stores the result? What's the maximum possible calculation?" Then test near that maximum.

Documenting Boundary Tests

A professional boundary test table format:

ID	Field	Input	Expected
BT-01	Quantity	0	Reject: below minimum
BT-02	Quantity	1	Accept
BT-03	Quantity	5	Accept + 10% discount
BT-04	Quantity	10	Accept
BT-05	Quantity	11	Reject: above maximum

Leave the "Actual" and "Status" columns to fill in during test execution.

Key Takeaways

Apply BVA to every field's minimum, maximum, and any business-rule thresholds
Calculated outputs have their own boundaries — test those too
Document tests before executing to avoid unconscious confirmation bias
The discount/trigger boundary is as important as the min/max boundary