Fix for #848 (not_constant fails within groups with 1 element)

[igor-lobanov-maersk]

resolves #848

This is a:

• documentation update
• bug fix with no breaking changes
• new functionality
• a breaking change

All pull requests from community contributors should target the main branch (default).

Description & motivation

As described in the bug report for #848, not_constant generic test fails when grouping is used and one of the groups has only one element. The implementation considers the value of this one element constant and fails the test. Whilst such interpretation is technically correct, the context where such test is used a different interpretation arguably would be preferable. I provided additional details in the bug report.

Checklist

• This code is associated with an Issue which has been triaged and accepted for development. Not really, I just filed a bug report, but found it's trivial to fix
• I have verified that these changes work locally on the following warehouses (Note: it's okay if you do not have access to all warehouses, this helps us understand what has been covered) I only have access to Dremio environment, and I tested it there
  • BigQuery
  • Postgres
  • Redshift
  • Snowflake
• I followed guidelines to ensure that my changes will work on "non-core" adapters by:
  • dispatching any new macro(s) so non-core adapters can also use them (e.g. the star() source) N/A
  • using the limit_zero() macro in place of the literal string: limit 0 N/A
  • using dbt.type_* macros instead of explicit datatypes (e.g. dbt.type_timestamp() instead of TIMESTAMP N/A
• I have updated the README.md (if applicable) N/A
• I have added tests & descriptions to my models (and macros if applicable) No, see below
• I have added an entry to CHANGELOG.md

I did not add a test, because it's not clear to me how such tests are written. There is no prior test for not_constant macro to extend. That said, I'm happy to write one with some guidance from the core team.

[github-actions]

This PR has been marked as Stale because it has been open with no activity as of late. If you would like the PR to remain open, please comment on the PR or else it will be closed in 7 days.

[dbeatty10]

@igor-lobanov-maersk many apologies for the delayed review here!

Could you add a test case for the scenario that your PR is fixing? That way we can confirm it fails without your fix but succeeds afterwards.

Here's an example:

• dbt-utils/integration_tests/data/schema_tests/data_test_not_constant.csv

  Lines 1 to 4 in 9237ba9

  	col_a,field
  	1,1
  	1,1
  	1,2

• dbt-utils/integration_tests/models/generic_tests/schema.yml

  Lines 4 to 10 in 9237ba9

  	- name: data_test_not_constant
  	columns:
  	- name: field
  	data_tests:
  	- dbt_utils.not_constant
  	- dbt_utils.not_constant:
  	group_by_columns: ['col_a']