Side Effect Check

Analyze PHP code for side effects that reduce testability.

Side Effect Types

1. State mutation — Changing object/array state
2. Global access — Reading/writing global variables
3. I/O operations — File, network, database
4. Output — echo, print, header
5. External service calls — API, queue, cache

Detection Patterns

1. State Mutation

// SIDE EFFECT: Mutates input
public function normalize(array &$data): void