diff

Compare legacy and modern system behavior to verify parity.

Usage

npx modernizespec diff [options]

What It Does

1. Reads parity-tests.json for baseline locations and test suites
2. Runs the specified test commands for each context
3. Compares outputs against legacy baselines
4. Reports deviations with field-level detail

Options

Flag	Description	Default
--dir <path>	Project directory	Current directory
--context <name>	Compare a specific context only	All contexts
--tolerance <n>	Numeric precision tolerance	0.001
--json	Output diff as JSON	Human-readable
--baseline <path>	Override baseline directory	From parity-tests.json

Examples

Diff All Contexts

npx modernizespec diff

Diff Specific Context

npx modernizespec diff --context Accounts

With Custom Tolerance

npx modernizespec diff --tolerance 0.01

Output

Parity Diff — Accounts
Baseline: legacy-snapshots/accounts/
Tests: 72 total

  ✓ 68 tests match baseline
  ✗ 4 tests deviate

Deviations:
  tax_inclusive_rounding:
    Legacy:  1,847.46
    Modern:  1,847.47
    Delta:   +0.01 (precision difference)

  advance_payment_allocation:
    Legacy:  allocated_amount = 5,000.00
    Modern:  allocated_amount = 4,999.99
    Delta:   -0.01 (rounding order difference)

Summary: 94.4% parity (threshold: 95.0%)
Status: ⚠ Below threshold — review deviations

Exit Codes

Code	Meaning
0	Parity meets or exceeds threshold
1	Parity below threshold
2	Baseline or spec files not found

See Also

• parity-tests.json Specification — Test inventory format
• export — Export diff results as HTML report