How can testing constraints be specified in dbt models?

The correct approach to specifying testing constraints in dbt models is by using the tests: keyword in the schema file or model definition. This method allows you to define tests that will ensure data integrity and quality directly within your dbt project.

Using tests: enables you to include various built-in tests such as uniqueness, not null, and relationships among models. This integration makes it straightforward to maintain and manage your tests alongside your model's definitions, providing clarity on which tests correspond to which models. It also supports the execution of these tests during the dbt run process, ensuring that data quality checks are part of your deployment workflow.

This method streamlines the testing process and promotes best practices by consolidating the tests within the schema file, which is specifically designed for defining metadata, including constraints and tests related to your models. This functionality is one of the key features of dbt that helps data teams to build reliable and trustworthy data models.