Add caveat about including all necessary given input fixtures for uni…

…t tests (#6603)

website/docs/docs/build/unit-tests.md

@@ -28,6 +28,7 @@ Starting in dbt Core v1.8, we have introduced an additional type of test to dbt
 - If your model has multiple versions, by default the unit test will run on *all* versions of your model. Read [unit testing versioned models](/reference/resource-properties/unit-testing-versions) for more information.
 - Unit tests must be defined in a YML file in your `models/` directory.
 - Table names must be [aliased](/docs/build/custom-aliases) in order to unit test `join` logic.
+- Include all [`ref`](/reference/dbt-jinja-functions/ref) or [`source`](/reference/dbt-jinja-functions/source) model references in the unit test configuration as `input`s to avoid "node not found" errors during compilation.
 - Redshift customers need to be aware of a [limitation when building unit tests](/reference/resource-configs/redshift-configs#unit-test-limitations) that requires a workaround. 
 
 Read the [reference doc](/reference/resource-properties/unit-tests) for more details about formatting your unit tests.