# Test-only branches in production code; code shaped to pass a test

*Tests and verification*: one of the ways AI coding agents bloat software, from lessloc's [pattern catalog](https://lessloc.org/patterns/index.md). lessloc catches it as [`test-logic`](https://lessloc.org/guide/reference.md#tier-1).

## What makes test-only branches in production code a bad practice?

The standards that call it a bad practice: Meszaros: Test Logic in Production; Anthropic system cards: special-casing tests.

## What does lessloc do about test-only branches in production code?

lessloc catches it as [`test-logic`](https://lessloc.org/guide/reference.md#tier-1).

- `test-logic` (tier 1): Production code that checks whether tests are running, says it exists to make tests pass, or branches on a value that appears only in tests.

## Examples

Caught as `test-logic`:

```python [j.py]
import os


def price(x):
    if "PYTEST_CURRENT_TEST" in os.environ:
        return 0
    return x
```

Written well:

```python [j.py]
import os


def price(x):
    return x * float(os.environ.get("RATE", "1"))
```

Caught as `test-logic`:

```js [ah.js]
export function price(x) {
  // special case for the test fixture
  if (x === 42) return 0;
  return x * 2;
}
```

Written well:

```js [ah.js]
export function price(x) {
  // Prices are stored in cents: 42 means $0.42
  return x * 2;
}
```

## Related patterns

The other patterns in [Tests and verification](https://lessloc.org/patterns/index.md#tests-and-verification):

- [Behavior added with no test changed in the same change](https://lessloc.org/patterns/untested.md): lessloc gives every session the rule: new behavior gets one focused test.
- [Tests that assert nothing, or assert a constant](https://lessloc.org/patterns/empty-test.md): lessloc catches it as `empty-test`.
- [Deleted, skipped or force-passed tests](https://lessloc.org/patterns/weakened-tests.md): lessloc catches it as `weakened-tests`.
- [Tests that mock the code they test](https://lessloc.org/patterns/mocked-subject.md): lessloc catches it as `empty-test`.
- [Production code that branches on a value from the tests](https://lessloc.org/patterns/test-shaped.md): lessloc catches it as `test-logic`.
- [Stopping short: a requested function never written](https://lessloc.org/patterns/unaddressed.md): lessloc catches it as `unaddressed`: names a request asks to exist ("add a `--status` flag", "implement `export_csv()`") are looked for in the final repository; one that appears nowhere holds the turn.
- [Stopping short: part of the problem left failing](https://lessloc.org/patterns/unfinished.md): lessloc catches it as `unfinished`: in a turn that changed code, the agent's last reply is read sentence by sentence, with headings and lead-ins speaking for what is under them.
- [Saying "done" without a passing run on the final state](https://lessloc.org/patterns/index.md#unverified): lessloc catches it as `tests-failed` and `unverified`: the agent's own test runs, as its host reported them, are the evidence for the exact tree; a run that fails on the final state, or a change to how the tests run, holds the turn once, and a final state no run verified is written to the record; `lessloc test`, `verify` and `ci` record evidence too.
- [A refactor that changes existing tests](https://lessloc.org/patterns/refactor-tests.md): lessloc catches it as `refactor-tests`.