Describe the bug

not_constant generic test would generate a false positive if used with group_by_column and there is only one row within a group

Steps to reproduce

Test model:

-- file test.sql
select 1 as a, 10 as b
union all
select 1 as a, 11 as b
union all
select 2 as a, 21 as b

Test schema.yml:

version: 2
models:
  - name: test
    columns:
      - name: b
        tests:
          - dbt_utils.not_constant:
              group_by_columns: ['a']

Run: dbt test -m test

Expected results

Test passes, because if there is only one value in the group, it does not break the constancy rule.

Actual results

Test fails.

Context

To explain what I'm doing and where this might be useful to others. I am flattening a nested array, and setting a flag if a given record is the first one. I wanted to add a test to make sure this logic always works, because I'm relying on this flag to be true exactly once for each id of the original record. In some cases there is only one element in the array, which gets the flag set to true correctly, but the test thinks it's wrong.

Screenshots and log output

Not sure what else would help.

System information

The contents of your packages.yml file:

packages:
  - package: dbt-labs/dbt_utils
    version: 1.1.1

Which database are you using dbt with?
Dremio

The output of dbt --version:

Core:
  - installed: 1.5.8
  - latest:    1.6.6 - Update available!

  Your version of dbt-core is out of date!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

Plugins:
  - dremio: 1.5.0 - Up to date!

Are you interested in contributing the fix?

PR provided #849