# Common Pitfalls

Translations: [Français](https://github.com/avajs/ava-docs/blob/master/fr_FR/docs/common-pitfalls.md)

## ESLint plugin

If you use [ESLint](http://eslint.org/), you can install [eslint-plugin-ava](https://github.com/avajs/eslint-plugin-ava). It will help you use AVA correctly and avoid some common pitfalls.

## AVA in Docker

If you run AVA in Docker as part of your CI, you need to fix the appropriate environment variables. Specifically, adding `-e CI=true` in the `docker exec` command. See [#751](https://github.com/avajs/ava/issues/751).

AVA uses [is-ci](https://github.com/watson/is-ci) to decide if it's in a CI environment or not using [these variables](https://github.com/watson/is-ci/blob/master/index.js).

## AVA and connected client limits

You may be using a service that only allows a limited number of concurrent connections. For example, many database-as-a-service businesses offer a free plan with a limit on how many clients can be using it at the same time. AVA can hit those limits as it runs multiple processes, but well-written services should emit an error or throttle in those cases. If the one you're using doesn't, the tests will hang.

Use the `concurrency` flag to limit the number of processes ran. For example, if your service plan allows 5 clients, you should run AVA with `concurrency=5` or less.

## Asynchronous operations

You may be running an asynchronous operation inside a test and wondering why it's not finishing. If your asynchronous operation uses promises, you should return the promise:

```js
test(t => {
	return fetch().then(data => {
		t.is(data, 'foo');
	});
});
```

Better yet, use `async` / `await`:

```js
test(async t => {
	const data = await fetch();
	t.is(data, 'foo');
});
```

If you're using callbacks, use [`test.cb`](https://github.com/avajs/ava#callback-support):

```js
test.cb(t => {
	fetch((err, data) => {
		t.is(data, 'foo');
		t.end();
	});
});
```

Alternatively, promisify the callback function using something like [`pify`](https://github.com/sindresorhus/pify):

```js
test(async t => {
	const data = await pify(fetch)();
	t.is(data, 'foo');
});
```

### Attributing uncaught exceptions to tests

AVA [can't trace uncaught exceptions](https://github.com/avajs/ava/issues/214) back to the test that triggered them. Callback-taking functions may lead to uncaught exceptions that can then be hard to debug. Consider promisifying and using `async`/`await`, as in the above example. This should allow AVA to catch the exception and attribute it to the correct test.

### Why are the enhanced assertion messages not shown?

Ensure that the first parameter passed into your test is named `t`. This is a requirement of [`power-assert`](https://github.com/power-assert-js/power-assert), the library that provides the enhanced messages.

```js
test(t => {
	t.is(1, 1);
});
```

---

Is your problem not listed here? Submit a pull request or comment on [this issue](https://github.com/avajs/ava/issues/404).