[Bug] Unit tests: macro fails when 'this' is passed as target_relation ('str' object has no attribute 'database')

[AliaksandraCherkas]

Is this a new bug in dbt-core?

• I believe this is a new bug in dbt-core
• I have searched the existing issues, and I could not find an existing issue for this bug

Current Behavior

When running dbt unit tests, a macro that works correctly during dbt run fails during unit test execution.

The failure happens when the macro receives this as an argument. In unit test context, this does not behave like a proper Relation object and does not expose attributes such as database, schema, or identifier.

As a result, macros that rely on Relation attributes fail with the error:

'str' object has no attribute 'database'

Expected Behavior

Unit tests should behave consistently with runtime execution (dbt run).

Specifically, one of the following should be true:

this resolves to a proper Relation object in unit tests, or

there is a documented and supported way to safely access Relation metadata in unit test context, or

macros can reliably detect unit test context and avoid breaking when accessing Relation attributes.

Steps To Reproduce

1.Create a model that calls a macro and passes this as an argument:

{{ detect_changes_braze(
    target_relation = this,
    source_table = ref('test_macro_detect_changes_braze_input'),
    compare_columns = ['external_id', 'updated_at', 'username', 'email', 'user_status']
) }}

2. Inside the macro, access Relation attributes, for example:

target_relation.database

3. Define a unit test for the model and use this as one of the test inputs:

- input: this

4. Run the unit test:

dbt test --select test_first_run_detect_changes_braze

5. Observe the compilation error:

'str' object has no attribute 'database'

Relevant log output

07:05:06  Failure in unit_test test_first_run_detect_changes_braze (tests\unit\fixtures\test_detect_changes_braze.yml)
07:05:06    Compilation Error in unit_test test_first_run_detect_changes_braze (tests\unit\fixtures\test_detect_changes_braze.yml)
  'str object' has no attribute 'database'

  > in macro detect_changes_braze (macros\detect_changes_braze.sql)
  > called by unit_test test_first_run_detect_changes_braze (tests\unit\fixtures\test_detect_changes_braze.yml)

Environment

- OS: Windows 11
- Python: 3.12.0
- dbt: 1.10.11

Which database adapter are you using with dbt?

bigquery

Additional Context

No response

[harishkesavarao]

Hello 👋, can I work on the issue please?