---
name: protest-covering-arrays
description: Use when you need to systematically test combinations of parameters, feature flags, configuration options, or input variations where interactions between settings could cause failures
---

# ProTest — Covering Array Generator

Generate minimal test matrices that cover all t-way parameter interactions. A covering array guarantees every pair (or triple, etc.) of parameter values appears in at least one test case, using far fewer cases than exhaustive testing. Research shows nearly all software failures are caused by interactions between 2-6 parameters.

## When to Use

- Testing combinations of configuration options, feature flags, or input parameters
- 3+ parameters with multiple values each where exhaustive testing is impractical
- You want pairwise (2-way) or higher-order coverage guarantees

## How to Run

```bash
protest generate -i model.cahtt -o results.csv
```

## Workflow

1. **Identify parameters** and their possible values from code or context
2. **Identify constraints** — invalid combinations (e.g., Safari only on Mac)
3. **Create a `.cahtt` model file** (see format below)
4. **Run:** `protest generate -i model.cahtt -o results.csv`
5. **Read `results.csv`** — each row is a test case

## Model File Format (.cahtt)

```json
{
  "Version": 1,
  "GlobalOrder": 2,
  "Parameters": [
    {
      "Name": "OS",
      "Values": [
        { "Name": "Windows", "Weight": 1, "IsNegative": false },
        { "Name": "Linux", "Weight": 1, "IsNegative": false }
      ]
    },
    {
      "Name": "Browser",
      "Values": [
        { "Name": "Chrome", "Weight": 2, "IsNegative": false },
        { "Name": "Firefox", "Weight": 1, "IsNegative": false }
      ]
    }
  ],
  "ConstraintText": "IF [OS] = \"Windows\" THEN [Browser] <> \"Safari\";",
  "Seeds": [
    { "OS": "Windows", "Browser": "Chrome" }
  ],
  "SubModels": []
}
```

**Weight** > 1 biases toward that value. **IsNegative** marks excluded values. **Seeds** are must-include rows. **SubModels** group parameters for higher-order coverage (`"Order": 3`).

## CLI Quick Reference

| Flag | Default | Purpose |
|------|---------|---------|
| `-i, --input` | required | Model file (.cahtt or .pict) |
| `-o, --output` | required | Output file (.csv, .md, .cahtt, .pict); repeatable |
| `--engine` | from model | `pict` or `sipo` |
| `--strength` | from model (2) | T-way coverage strength |
| `--trials` | 1000/10000 | Parallel trials (best result kept) |
| `--max-time` | no limit | Seconds before stopping |
| `--seed` | auto | Deterministic random seed |
| `--cores` | ~75% | Parallel cores |

Run with `generate --help` for all options.

## Example

```bash
protest generate -i model.cahtt -o results.csv --engine sipo --max-time 30
protest generate -i model.cahtt -o results.csv -o results.md
```