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# Assert That Event Processor

> For the full documentation index, see: https://docs.mulesoft.com/llms.txt

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The Assert That event processor allows you to run assertions to validate the state of a Mule event’s
content. You can use the Assert That processor to validate the Mule event after the production code
runs.

The Assert That processor uses a set of DataWeave functions called `MUnit matchers` to define the
assertion conditions for any value in an expression.

For example, to assert that a payload is equal to a certain value, configure the Assert That
processor using the `equalTo()` matcher.

```xml
<munit-tools:assert-that
  expression="#[payload]"
  is="#[MunitTools::equalTo('example')]"
  message="The payload should be ‘example’"/>
```

Or you can also check if the payload is null using the `nullValue()` matcher.

```xml
<munit-tools:assert-that
  expression="#[payload]"
  is="#[MunitTools::nullValue()]"
  message="The payload should be null"/>
```

See [MUnit Matchers](https://docs.mulesoft.com/munit/3.6/munit-matchers) for more information.

If these assertion fails, the processor throws a `java.lang.AssertionError`.

## See Also

- [MUnit Matchers](https://docs.mulesoft.com/munit/3.6/munit-matchers)