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_idcountry_code
1AU
2AU
......
1US
2US
......

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: unique_id
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