test-case-writing

name	test-case-writing
description	Skill for test case design — equivalence partitioning, boundary value analysis, test data builders, and test coverage strategy.
stage	testing
type	delivery-skill
version	3.0
category	delivery
scope	platform
tags	["methodology","testing","test-design"]

Test Case Writing Skill

Purpose

Guides systematic test case design to maximize defect detection with a manageable number of test cases.

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Equivalence Partitioning

Divide input domain into classes where all values produce the same behavior. Test at least one value from each partition.

Process

1. Identify input parameters
2. For each parameter, define valid and invalid partitions
3. Select one representative value from each partition
4. Combine partitions — one test case per interesting combination

Example: Order Quantity (valid range: 1-999)

Partition	Values	Expected	Test Value
Below minimum	< 1	Validation error	0
Valid range	1-999	Accepted	50
Above maximum	> 999	Validation error	1000
Null/missing	null	Validation error	null
Negative	< 0	Validation error	-1

Multi-Parameter Strategy

• Each-choice (minimum): one test per partition, ensuring each partition appears at least once
• Pairwise (thorough): all 2-way combinations of partitions

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Boundary Value Analysis

Bugs cluster at partition boundaries. Test exact boundary values and adjacent values.

For each boundary, test:

1. Value just below the boundary
2. The boundary value itself
3. Value just above the boundary

Boundary Types

• Numeric ranges: min-1, min, min+1, max-1, max, max+1
• String lengths: empty, 1, max-1, max, max+1
• Collection sizes: empty, 1, max-1, max, max+1
• Date ranges: day before start, start, end, day after end
• State transitions: just before trigger, at trigger, just after

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Test Coverage Strategy

Required Tests per Feature

1. Happy path: primary use case with typical input — verify return value, side effects, response format
2. Error paths: one test per exception type in the error hierarchy, one per HTTP error status
3. Edge cases: empty/null optionals, max values, unicode, concurrent access, timezone boundaries

Edge Case Categories

• Empty/null inputs for optional fields
• Maximum and minimum allowed values
• Unicode, special characters, very long strings
• Concurrent access patterns
• Timezone and locale boundaries
• Zero amounts, negative amounts
• Single-element and maximum-size collections

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Test Data Builders

Use the Builder pattern for test data with sensible defaults:

class OrderTestDataBuilder {
    private var id: UUID = UUID.randomUUID()
    private var status: OrderStatus = OrderStatus.PENDING
    private var items: MutableList<OrderItem> = mutableListOf()

    fun withStatus(status: OrderStatus) = apply { this.status = status }
    fun confirmed() = apply { this.status = OrderStatus.CONFIRMED }

    fun withSingleItem(
        quantity: Int = 1,
        unitPrice: BigDecimal = BigDecimal("9.99")
    ) = apply {
        items.add(OrderItem(quantity = quantity, unitPrice = unitPrice))
    }

    fun build(): Order = Order(id = id, status = status, items = items)
}

// Usage: anOrder().confirmed().withSingleItem().build()

Guidelines

1. Every field has a sensible default
2. Named factory: anOrder(), aCustomer(), aProduct()
3. Scenario methods: .confirmed(), .withExpiredPayment()
4. Each test creates its own data — avoid shared mutable state
5. Use UUIDs, not auto-increment IDs