Add unit test for a dbt model

Additional Resources

Spec Reference - All required and optional YAML keys for unit tests
Examples - Unit test examples across formats (dict, csv, sql)
Incremental Models - Unit testing incremental models
Ephemeral Dependencies - Unit testing models depending on ephemeral models
Special Case Overrides - Introspective macros, project variables, environment variables
Versioned Models - Unit testing versioned SQL models
BigQuery Caveats - BigQuery-specific caveats
BigQuery Data Types - BigQuery data type handling
Postgres Data Types - Postgres data type handling
Redshift Caveats - Redshift-specific caveats
Redshift Data Types - Redshift data type handling
Snowflake Data Types - Snowflake data type handling
Spark Data Types - Spark data type handling