refactoring

name: refactoring description: Safe code refactoring with test protection and incremental changes. Improves structure without changing behavior. Use when extracting methods, reducing duplication, or restructuring code.

Behavior-preserving code transformation protected by tests.

Core Principle

Tests must pass before AND after every change.

When to Use

Reducing duplication (DRY)
Extracting methods/classes
Improving naming and readability
Simplifying complex conditionals
Preparing code for new features

MCP Workflow

# 1. Understand current structure
serena.get_symbols_overview(relative_path="target/file")

# 2. Check all usages before change
serena.find_referencing_symbols(name_path="TargetClass/method")

# 3. Verify test coverage (TOKEN CRITICAL - Always limit!)
serena.search_for_pattern(
    substring_pattern="test.*TargetClass",
    relative_path="test/",
    context_lines_after=1,
    max_answer_chars=3000
)

# 4. Get target code
serena.find_symbol(name_path="TargetClass/method", include_body=True)

# 5. Safe rename
serena.rename_symbol(name_path="oldName", relative_path="file", new_name="newName")

Workflow

1. Prepare

- Ensure tests exist and pass
- Identify refactoring scope
- Plan incremental steps

2. Refactor (small steps)

For each change:
  1. Make one refactoring move
  2. Run tests immediately
  3. If PASS: commit
  4. If FAIL: revert, try smaller step

3. Verify

- Run full test suite
- Review final structure
- Update docs if needed

Common Patterns

Extract Method

When: Function too long or has multiple responsibilities

BEFORE:
processOrder(order):
    # validate (10 lines)
    # calculate shipping (10 lines)
    # save (5 lines)

AFTER:
processOrder(order):
    validateOrder(order)
    shipping = calculateShipping(order)
    repository.save(order.copy(shipping=shipping))

Extract Class

When: Class has too many responsibilities

OrderService with 6 methods
    -> OrderService (orchestration)
    -> OrderCalculator (calculations)
    -> OrderNotifier (notifications)

Replace Conditional with Polymorphism

When: Repeated switch/if-else on type

BEFORE:
switch customer.type:
    case "REGULAR": return total * 0.05
    case "PREMIUM": return total * 0.10

AFTER:
interface CustomerType { calculateDiscount(total) }
class RegularCustomer implements CustomerType { ... }
class PremiumCustomer implements CustomerType { ... }

Simplify Conditionals

BEFORE:
if a:
    if b:
        if c:
            return true
return false

AFTER:
return a and b and c

Output Format

## Refactoring: [Target]

| Item | Value |
|------|-------|
| Target | ClassName.method |
| Type | Extract / Rename / Simplify |
| Usages | N references |
| Tests | X tests covering |

### Steps
1. [Description] - Tests: PASS
2. [Description] - Tests: PASS

### Result
Files: N | Changes: +X/-Y | Tests: PASS

Safety Checklist

Tests exist and pass before starting
Each step is independently committable
No behavior changes
All references updated
Tests still pass after completion

When NOT to Refactor

No test coverage (add tests first)
Under time pressure (do minimal fix)
Code is about to be deleted
Not sure about desired outcome