You have created a model called stg_tasks and now you need to implement tests.

In dbt, when you configure a generic test like not_null in YAML, the configuration for that test must be a mapping, not another list item. The correct structure is:

tests:

- not_null:

config:

where: "state = 'completed'"

In your original YAML, you wrote:

tests:

- not_null:

- config:

where: "state = 'completed'"

The extra dash (- config) makes config an element of a list rather than a key under the not_null test. This breaks the expected shape of the test definition. When dbt parses the schema.yml, it fails to correctly interpret the patch for the stg_tasks model, which leads to the warning: “Did not find matching node for patch with name 'stg_tasks'…”.

By removing the extra dash and nesting config directly under not_null, dbt now reads this as a single generic test named not_null with a config block that passes the where argument. This allows dbt to correctly attach the test to the completed_at column of the stg_tasks model and eliminates the compiler warning.

Therefore, Option B is the only structurally valid configuration and is the correct answer.