# Reproduce Reduce Regress

> Systematic workflow for debugging by reproducing bugs with real data, reducing test cases to minimal examples, and adding regression tests Use when this capability is needed.

- Skill: `tomevault-io/reproduce-reduce-regress` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/reproduce-reduce-regress`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/reproduce-reduce-regress/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Productivity
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/reproduce-reduce-regress

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# Reproduce, Reduce, Regress

When debugging a bug, follow this workflow:

## 1. Reproduce

**Goal:** Get a failing test that demonstrates the bug using REAL data.

- Copy the EXACT input that triggers the bug (don't paraphrase or simplify yet)
- Use the EXACT types/structs from the failing code
- Verify the test actually fails with the same error message

## 2. Reduce

**Goal:** Find the MINIMAL input that still triggers the bug.

- Create MULTIPLE test variants, don't comment things in/out
- Name them descriptively: `test_minimal_one_field`, `test_with_queries`, etc.
- Binary search: remove half the input, see if it still fails
- Keep narrowing until you find the smallest failing case
- Also find a PASSING case that's as close as possible to the failing one

The difference between your minimal failing case and your minimal passing case IS the bug.

## 3. Regress (Regression Tests)

**Goal:** Ensure the bug never comes back.

- Keep ALL your test variants - both passing and failing
- The failing ones become regression tests after the fix
- The passing ones document expected behavior
- Name tests after the issue number: `test_issue_1356_*`

## Anti-patterns

❌ Commenting code in/out to test different scenarios
❌ Modifying a single test repeatedly
❌ "Simplifying" input without verifying the bug still reproduces
❌ Deleting test variants after finding the bug
❌ Theorizing about what MIGHT cause the bug before reproducing

## Example Structure

```rust
// Minimal failing case
#[test]
fn test_issue_1356_fails_without_queries_default() { ... }

// Minimal passing case (shows the workaround)
#[test]
fn test_issue_1356_passes_with_queries_default() { ... }

// Original reproduction from user's code
#[test]
fn test_issue_1356_full_reproduction() { ... }
```

---
> Source: [facet-rs/facet](https://github.com/facet-rs/facet) — distributed by [TomeVault](https://tomevault.io).
<!-- tomevault:4.0:skill_md:2026-06-27 -->