Assertion plans ensure tests only pass when a specific number of assertions have been executed. They'll help you catch cases where tests exit too early. They'll also cause tests to fail if too many assertions are executed, which can be useful if you have assertions inside callbacks or loops.
If you do not specify an assertion plan, your test will still fail if no assertions are executed. Set the `failWithoutAssertions` option to `false` in AVA's [`package.json` configuration](./06-configuration.md) to disable this behavior.
Note that, unlike [`tap`](https://www.npmjs.com/package/tap) and [`tape`](https://www.npmjs.com/package/tape), AVA does *not* automatically end a test when the planned assertion count is reached.
These examples will result in a passed test:
```js
test('resolves with 3', t => {
t.plan(1);
return Promise.resolve(3).then(n => {
t.is(n, 3);
});
});
```
These won't:
```js
test('loops twice', t => {
t.plan(2);
for (let i = 0; i <3;i++){
t.true(i <3);
}
}); // Fails, 3 assertions are executed which is too many
test('invokes callback synchronously', t => {
t.plan(1);
someAsyncFunction(() => {
t.pass();
});
}); // Fails, the test ends synchronously before the assertion is executed
```
## Skipping assertions
Any assertion can be skipped using the `skip` modifier. Skipped assertions are still counted, so there is no need to change your planned assertion count.
```js
test('skip assertion', t => {
t.plan(2);
t.is.skip(foo(), 5); // No need to change your plan count when skipping
t.is(1, 1);
});
```
## Custom assertions
You can use any assertion library instead of or in addition to the built-in one, provided it throws exceptions when the assertion fails.
This won't give you as nice an experience as you'd get with the [built-in assertions](#built-in-assertions) though, and you won't be able to use the [assertion planning](#assertion-planning) ([see #25](https://github.com/avajs/ava/issues/25)).
You'll have to configure AVA to not fail tests if no assertions are executed, because AVA can't tell if custom assertions pass. Set the `failWithoutAssertions` option to `false` in AVA's [`package.json` configuration](./06-configuration.md).
Assert that `actual` is the same as `expected`. This is based on [`Object.is()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is).
Assert that `actual` is not the same as `expected`. This is based on [`Object.is()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is).
Assert that `actual` is like `selector`. This is a variant of `.deepEqual()`, however `selector` does not need to have the same enumerable properties as `actual` does.
Instead AVA derives a *comparable* value from `actual`, recursively based on the enumerable shape of `selector`. This value is then compared to `selector` using `.deepEqual()`.
In the following example, the `map` property of `actual` must be deeply equal to that of `selector`. However `nested.qux` is ignored, because it's not in `selector`.
Assert that an error is thrown. `fn` must be a function which should throw. By default, the thrown value *must* be an error. It is returned so you can run more assertions against it.
Assert that an error is thrown. `thrower` can be an async function which should throw, or a promise that should reject. This assertion must be awaited.
The implementation function behaves the same as any other test function. You can even use macros. The first title argument is always optional. Additional arguments are passed to the implementation or macro function.
`.try()` is an asynchronous function. You must `await` it. The result object has `commit()` and `discard()` methods. You must decide whether to commit or discard the result. If you commit a failed result, your test will fail. Calling `commit()` on a failed result will throw an error.
You can check whether the attempt passed using the `passed` property. Any assertion errors are available through the `errors` property. The attempt title is available through the `title` property.
Logs from `t.log()` are available through the `logs` property. You can choose to retain these logs as part of your test by passing `{retainLogs: true}` to the `commit()` and `discard()` methods.
The implementation function receives its own [execution context](./02-execution-context.md), just like a test function. You must be careful to only perform assertions using the attempt's execution context. At least one assertion must pass for your attempt to pass.
You may run multiple attempts concurrently, within a single test. However you can't use snapshots when you do so.
