Edge Case Enumeration

Edge Case Enumeration

Purpose

Systematically discover edge cases for proposed features using structured enumeration techniques.

Inputs

• Feature specification or user story being analyzed
• Input fields and their expected types/formats
• State transitions and lifecycle of the feature
• User roles and permission model

Process

Step 1: Identify Input Boundaries

For each input: document the type, valid range, length constraints, format requirements, and whether it's required or optional.

Step 2: Apply Boundary Value Analysis

For each input, enumerate:

• Empty/null/undefined: What happens with no input, null, undefined, empty string, whitespace-only?
• Minimum and maximum values: At the boundary, one below, one above
• Just inside and just outside valid ranges: Off-by-one errors, boundary transitions
• Special characters: Unicode (CJK, Arabic, RTL text), emoji, zero-width characters, combining characters, null bytes
• Extremely long inputs: Past max length, at max length, strings that look like numbers

Step 3: Enumerate State Combinations

• Empty state: First use, no data created yet, fresh account
• Partial state: Incomplete setup, mid-operation interruption, partially filled forms
• Full state: At capacity limits, pagination boundaries, maximum items reached
• Stale state: Cached data from previous version, outdated references, deleted dependencies

Step 4: Analyze Concurrent Scenarios

• Same user simultaneous ops: Double submit, rapid clicks, multiple tabs, back button after submit
• Different users on same resource: Concurrent edits, delete while viewing, permission change during session
• Operations during deployment/migration: Request in flight during deploy, schema change mid-operation

Step 5: Consider Temporal Edge Cases

• Timezone boundaries: UTC midnight, DST transitions, user in different timezone than server
• Session expiry mid-operation: Token expires during long form fill, refresh token rotation
• Long-running operations: Timeout during processing, progress loss on reconnect, orphaned background jobs

Step 6: Map Permission Edge Cases

• Role transitions: Admin demoted to user during active session, role upgrade without re-login
• Shared resources with mixed permissions: Viewer accessing editor's link, public/private toggle
• Deleted/suspended user data: References to deleted users, suspended account data visibility, orphaned content

Output Format

Edge Case Table

Input Edge Cases

State Edge Cases

Concurrency Edge Cases

Temporal Edge Cases

Permission Edge Cases

Priority Key

• P0: Will break in production, must handle before launch
• P1: Likely to occur, causes poor UX or data issues
• P2: Unlikely but possible, handle if time permits

Quality Checks

• Every input field has boundary value analysis
• Empty/null/error states are covered for all inputs
• Concurrent scenarios are addressed for shared resources
• At least 5 edge cases per category (input, state, concurrency, temporal, permission)
• Each edge case has defined expected behavior
• P0 cases are flagged for immediate implementation

Evolution Notes