[CT-3129] Ability to test the incremental behavior of models using incremental strategy that requires partitioning

[gshank]

Description

Ability to test the incremental behavior of models using an incremental strategy that requires partitioning (insert_overwrite or delete+insert). See #8422.

If I have an incremental model that uses a strategy that uses "partitioning":

{{
  config(
    materialized='incremental',
    unique_key='date_day',
    incremental_strategy='insert_overwrite',
    ...
  )
}}

select
    date_trunc('day', event_at) as date_day,
    count(distinct user_id) as daily_active_users

from {{ ref('events') }} 

{% if is_incremental() %}

  -- this filter will only be applied on an incremental run
  -- (uses >= to include records arriving later on the same day as the last run of this model)
  where date_day >= (select max(date_day) from {{ this }})

{% endif %}

group by 1

I should be able to add a unit test to this model and have it work as expected.

unit_tests:
  - name: my_favorite_unit_test
    model: my_incremental_model
    given:
      - input: ref('events')
        format: csv
        fixture: my_events_input_fixture
      - input: this
        format: csv
        fixture: my_incremental_model_this_fixture
    expect:
      format: csv
      fixture: my_incremental_model_output_fixture
    overrides: 
      macros:
        is_incremental: true 

Acceptance Criteria

Unit testing of incremental models with insert_overwrite or delete+insert strategy.

Impact to Other Teams

None

Will backports be required?

No

Context

[ChenyuLInx]

blocked on #8499