# Behavior added with no test changed in the same change

*Tests and verification*: one of the ways AI coding agents bloat software, from lessloc's [pattern catalog](https://lessloc.org/patterns/index.md). lessloc gives every session the rule: new behavior gets one focused test.

## What makes behavior added with no test changed in the same change a bad practice?

The standard that calls it a bad practice: Google engineering practices: tests ship with the change they test.

## What does lessloc do about behavior added with no test changed in the same change?

lessloc gives every session the rule: new behavior gets one focused test. lessloc catches it as [`untested`](https://lessloc.org/guide/reference.md#tier-1). It is not raised for refactors, for fixes that do not grow the code, or for projects without tests.

- `untested` (tier 1): The change adds behavior and no test changed, [with some exceptions](https://lessloc.org/guide/how-it-works.md#end-of-turn-unfinished-work-is-held-once).

## Related patterns

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

- [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`.
- [Test-only branches in production code](https://lessloc.org/patterns/test-logic.md): lessloc catches it as `test-logic`.
- [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`.