[Bug] Unit Test fails when using adapter get_relation function

[mithungame]

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

Currently we have an existing macro where we alter SQL behavior based on presence or absence of a model

  {%- set relation = adapter.get_relation(this.database, this.schema, this.table) -%}
  {%- set target_table = model.get('alias', model.get('name')) -%}
  {%- set target_relation_exists, target_relation = get_or_create_relation(database=this.database,schema=this.schema,identifier=target_table,type='table') -%}
  {%- if not target_relation_exists -%}
 < do what needs to be done for first creation >
  {%- else -%}
< do what needs to be done for subsequent creation >

The code works fine without any issue

When trying to unit test this model it fails with below error
'str object' has no attribute 'database'.

unit_tests:
  - name: test_dimension
    model: target_dim
    overrides:
      macros:
        is_incremental: true
    given:
      - input: ref('stage_table')
        rows:
          ... rows here
      - input: this
        rows:
          ... rows here
    expect:
      rows:
        ... rows here

narrowed it down to usage of the below line
{%- set relation = adapter.get_relation(this.database, this.schema, this.table) -%}

Expected Behavior

The "this" in adapter is treated as a string rather than a relation .
using {{ this }} in schema yml is not possible
the "this" inside adapter relation should be a relation

Steps To Reproduce

create below model and unit test

{{
    config(
        materialized='incremental'
    )
}}
{% if execute %}
{%- set relation = adapter.get_relation(this.database, this.schema, this.table) -%}
{% endif %}


select * from {{ ref('temp_table') }}
where event_time > (select max(event_time) from {{ this }})

Relevant log output

13:33:27  Running with dbt=1.8.3
13:33:28  Registered adapter: snowflake=1.8.3
13:33:29  Found 27 models, 15 data tests, 13 sources, 601 macros, 2 unit tests
13:33:29
13:33:32  Concurrency: 5 threads (target='dev')
13:33:32
13:33:32  1 of 1 START unit_test temp::my_incremental_model_incremental_mode .......... [RUN]
13:33:33  1 of 1 ERROR temp::my_incremental_model_incremental_mode .................... [ERROR in 0.09s]
13:33:33
13:33:33  Finished running 1 unit test in 0 hours 0 minutes and 3.81 seconds (3.81s).
13:33:33
13:33:33  Completed with 1 error and 0 warnings:
13:33:33
13:33:33    Compilation Error in unit_test my_incremental_model_incremental_mode (models\schema.yml)
  'str object' has no attribute 'database'. This can happen when calling a macro that does not exist. Check for typos and/or install package dependencies with "dbt deps".
13:33:33
13:33:33  Done. PASS=0 WARN=0 ERROR=1 SKIP=0 TOTAL=1

Environment

- OS: windows
- Python: 3.11
- dbt: 1.8.3

Which database adapter are you using with dbt?

snowflake

Additional Context

No response

[devmessias]

Maybe has the same cause as #10139.

This part

select * from {{ ref('temp_table') }}
where event_time > (select max(event_time) from {{ this }})

should be working because is covered by a functional test on dbt-core

dbt-core/tests/functional/unit_testing/fixtures.py

Lines 302 to 304 in a0674db

	{% if is_incremental() %}
	where event_time > (select max(event_time) from {{ this }})
	{% endif %}

[mithungame]

Yes, the {{this}} works as mentioned
But when the same "this" is invoked in adapter get relation function it is treated not as a relation object but rather as a plain string. The interpretation of "this" is not consistent

[devmessias]

I think this is a limitation of unit tests already pointed here in some reported bugs. We should have an option to override dynamic variables in jinja template like this

overrides:
    dynamic_vars:
         target_relation_exists = true