You can use the assert shape is typically used for testing purposes -you can define a static payload which is used to validate that the current payload (i.e. the payload generated up to the point that the assert shape is encountered) is as expected.
To view/update the settings for an existing assert shape, click the associated 'cog' icon:
This opens the options panel - for example:
To configure an assert shape, all you need to do is paste the required payload and save the shape for example:
An assert shape can only be saved if a payload is present. If you add an assert payload shape but don't have the required payload immediately to hand, you can just enter {}and save.
