Defining multiple unique keys

I would like to define multiple unique tests on 1 model but got following compilation error :
Running with dbt=0.20.1
Encountered an error:
Compilation Error
Invalid test config given in models/tableau/zrshop.yml:
test definition dictionary must have exactly one key, got [(‘unique’, None), (‘severity’, ‘error’)] instead (2 keys)
@: UnparsedNodeUpdate(original_file_path='model…ne)

This code produces a similar error.
1 - name: stg_orders
2 columns:
3 - name: customer_id
4 tests:
5 - relationships:
6 to: ref(‘customers’)
7 field: customer_id
test definition dictionary must have exactly one key, got [(‘relationships’, None), (‘to’, “ref(‘customers’)”), (‘field’, ‘customer_id’)] instead (3 keys)
I determined that the indention on lines 6 and 7 was causing the problem.
BTW, an easy way to capture the error message is to attempt to run a Select using a statement tab.