> ## Documentation Index
> Fetch the complete documentation index at: https://docs.thrindex.com/llms.txt
> Use this file to discover all available pages before exploring further.

# E0205 — TestSetTooSmall

> The conformance harness requires at least 100 samples. Fewer samples cannot statistically characterize the metric distribution.

<Warning>E0205: test set too small</Warning>

## What happened

You ran `thrindex bench --conformance` with fewer than 100 fixture samples. The conformance harness requires a minimum of 100 samples (as specified in `CONFORMANCE_ENVELOPE_V0.min_test_samples`).

## Why

The conformance metric is a distribution: `T_mean`, `T_max` (99th percentile), and `P_pred` are statistics computed over many samples. With fewer than 100 samples:

* The 99th percentile estimate is unstable (one sample is the 99th percentile)
* `P_pred` has a confidence interval too wide to be meaningful
* The result would not be statistically valid evidence of conformance

## How to fix

1. **Provide at least 100 fixture samples**: the frozen fixture set at `conformance/fixtures/` contains 120 SHD samples — always use the full set.
2. Do not pass `--n-samples` with a value below 100 in production conformance runs.
3. For development/debugging, a structural demo with fewer samples is acceptable, but the harness will report `STRUCTURAL DEMO — not a certification run` rather than a PASS/FAIL verdict.

## Example

```
E0205: test set too small — 50 samples provided, minimum is 100
Why: fewer samples than the envelope's `min_test_samples` cannot statistically characterise the metric distribution
Fix: provide ≥100 samples; see ADR-0010 Part II for the ratification measurement specification
Docs: https://docs.thrindex.com/errors/E0205
```