Can I test the uniqueness of two columns?

Yes, There's a few different options.

Consider an orders table that contains records from multiple countries, and the combination of ID and country code is unique:

order_id	country_code
1	AU
2	AU
...	...
1	US
2	US
...	...

Here are some approaches:

1. Create a unique key in the model and test that

models/orders.sql

select
  country_code || '-' || order_id as surrogate_key,
  ...

models/orders.yml

version: 2

models:
  - name: orders
    columns:
      - name: surrogate_key
        tests:
          - unique

2. Test an expression

models/orders.yml

version: 2

models:
  - name: orders
    tests:
      - unique:
          column_name: "(country_code || '-' || order_id)"

3. Use the dbt_utils.unique_combination_of_columns test

This is especially useful for large datasets since it is more performant. Check out the docs on packages for more information.

models/orders.yml

version: 2

models:
  - name: orders
    tests:
      - dbt_utils.unique_combination_of_columns:
          combination_of_columns:
            - country_code
            - order_id