# Tests that mock the code they 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 [`empty-test`](https://lessloc.org/guide/reference.md#tier-1).

## What makes tests that mock the code they test a bad practice?

The standard that calls it a bad practice: Carr, TDD anti-patterns: The Mockery.

## What does lessloc do about tests that mock the code they test?

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

- `empty-test` (tier 1): A test that asserts nothing or only a constant, or one that mocks the code it tests.

## Examples

Caught as `empty-test`:

```python [tests/test_cr.py]
from unittest.mock import patch


@patch("shop.pay.charge")
def test_charge(mock_charge):
    mock_charge.return_value = 1
    assert charge(5) == 1
```

Written well:

```python [tests/test_cr.py]
from unittest.mock import patch


@patch("shop.pay.send_receipt")
def test_charge(mock_send):
    assert charge(5) == 5
    mock_send.assert_called_once()
```

Caught as `empty-test`:

```js [cart.test.js]
import { test, vi } from "vitest";
import { total } from "./cart";
vi.mock("./cart");
test("total", () => {
  expect(total([1])).toBe(1);
});
```

Written well:

```js [cart.test.js]
import { test, vi } from "vitest";
import { total } from "./cart";
vi.mock("./prices");
test("total", () => {
  expect(total([1])).toBe(1);
});
```

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