Relationship test is not triggered

[leoch20]

Describe the bug

The relationship test does not get triggered

Steps To Reproduce

models/child.sql

select 1 as parent_id, 1 as val
union
select 2 as parent_id, 2 as val

models/parent.sql

select 1 as id, 1 as val

models/test.yml

models:
  - name: child
    columns:
      - name: parent_id
        tests:
          - relationships:
              to: ref('parent')
              field: id

  - name: parent
    columns:
      - name: id

Create the models:
dbt run -m parent child

Expected behavior

Running dbt test -m child should error out, but it does not. Although, running dbt test -m parent child does error out.

Screenshots and log output

WARNING: Nothing to do. Try checking your model configs and model specification args

System information

Which database are you using dbt with?

• postgres
• redshift
• bigquery
• snowflake
• other (specify: ____________)

The output of dbt --version:

installed version: 0.20.1
   latest version: 0.20.2

Your version of dbt is out of date! You can find instructions for upgrading here:
https://docs.getdbt.com/docs/installation

Plugins:
  - bigquery: 0.20.1
  - snowflake: 0.20.1
  - redshift: 0.20.1
  - postgres: 0.20.1

The operating system you're using:

macOS Big Sur | version 11.4

The output of python --version:

Python 3.8.8

[jtcohen6]

@leoch20 We made a change in dbt v0.20 around test selection that caught a few folks by surprise (#3496, #3571). I'd recommend you read #3571 (comment) for a quick summary.

To make a long story short, we believe that dbt test -m parent child should absolutely run the relationship test defined between them; but dbt test -m parent or dbt test -m child alone should not presume that you want to include a test with an unselected parent.

The mistake here, for which I take full responsibility, was the subtlety of this change, and the lack of transparency when a familiar command produced a suddenly unfamiliar result. To that end, dbt v0.21 will include better logging around which tests have been excluded because of an unselected parent, as well as an optional --greedy flag that lets you revert to the previous behavior of "greedier" test selection (#3723, #3833).