edge-case-coverage

Edge Case Coverage

Systematically identify and handle boundary conditions.

Edge Case Categories

Category	Examples
Boundary	0, 1, max, min, empty
Input	null, undefined, wrong type
State	uninitialized, concurrent, stale
Resource	timeout, no memory, disk full
Network	offline, slow, partial failure
Permission	unauthorized, expired, revoked

Boundary Analysis

Numeric Boundaries

Value: age
├── Below min: -1
├── At min: 0
├── Just above min: 1
├── Normal: 25
├── Just below max: 119
├── At max: 120
└── Above max: 121

String Boundaries

Value: username
├── Empty: ""
├── Single char: "a"
├── Max length: "a" * 255
├── Over max: "a" * 256
├── Special chars: "user@#$"
└── Unicode: "user"

Error Scenario Template

## Scenario: [Name]

**Trigger**: [What causes it]
**Symptoms**: [What user sees]
**Root cause**: [Why it happens]
**Prevention**: [How to avoid]
**Recovery**: [How to fix]

Validation Checklist

Input Validation

• Required fields present
• Type correct
• Format valid (email, URL, etc.)
• Range within bounds
• Length within limits
• Characters allowed

State Validation

• Object initialized
• Resources available
• Permissions granted
• Dependencies met
• No conflicts

Coverage Matrix

Input	Valid	Empty	Null	Overflow	Malformed
Name	[x]	[x]	[x]	[x]	[x]
Email	[x]	[x]	[x]	[x]	[x]
Age	[x]	[x]	[x]	[x]	[x]

Anti-Patterns

• Happy path only
• Ignoring nulls
• Assuming valid input
• Missing timeout handling
• Silent failures