function_categories.md

Function Categorization Guide

Categorization Dimensions

1. By Responsibility

Category	Keywords	Examples
Parsing/Encoding	parse, decode, serialize, deserialize	parseFrame(), decodeHeader()
Network I/O	send, receive, read, write, connect	asyncRead(), sendPacket()
State Management	set, get, update, transition	setState(), getStatus()
Callback/Event	on, callback, handler, notify	onDataReceived(), handleEvent()
Utility/Conversion	to, from, convert, format	toBigEndian(), formatTime()
Lifecycle	init, start, stop, close, reset	initialize(), shutdown()

2. By Complexity

Grade	Features	Test Strategy
Simple	Pure functions, no side effects	Unit testing, parameterized testing
Medium	Dependent on internal state	Fixture + State verification
Complex	Async, multi-threaded, I/O	Mocking + Integration testing

3. By Risk Level

Grade	Identification	Testing Requirement
High Risk	Security related, calculations, protocols	100% branch coverage
Medium Risk	Business logic, state machines	Main path + Boundaries
Low Risk	Logging, formatting, helpers	Basic functional verification

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Priority Decision Tree

Does the function handle external input?
├── Yes → Parsing/Network → P0 (Highest Priority)
│   └── Boundary values, malicious input, fuzzing
└── No → Does it affect core flow?
    ├── Yes → Business logic → P1
    │   └── State transitions, exception handling
    └── No → Does it have side effects?
        ├── Yes → I/O operation → P2
        │   └── Mocking, integration testing
        └── No → Utility function → P3
            └── Boundary condition verification

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Identification Patterns

High Priority Function Features

// P0: Directly handles external data
bool parse(const uint8_t* data, size_t len);
Result decode(std::span<const std::byte> buffer);

// P1: State transitions
void transition(State newState);
bool handleMessage(MessageType type);

// P2: I/O operations
void asyncRead(ReadCallback cb);
bool sendData(const Buffer& buf);

Low Priority Function Features

// P3: Pure utility functions
std::string formatTime(time_t t);
uint32_t crc32(const void* data, size_t len);

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Function Signature Analysis

Input Type Hints

Parameter Type	Hint	Test Focus
const uint8_t*	Raw byte stream	Boundaries, endianness
std::span<>	Buffer	Empty span, out of bounds
std::string_view	Text input	Empty string, Unicode
enum	State/Type	Invalid enum values

Return Type Hints

Return Type	Hint	Test Focus
bool	Success/Failure	Both paths covered
std::optional<T>	May have no result	std::nullopt case
Result<T, Error>	Error handling	All error codes
void	Side effects	State change verification