seeing no-op tests, and other basic Elementary questions

[stephendewey-se]

I have some questions about how Elementary works under the hood:

• When you create a new test, does it only start collecting the data needed for the test at that time, or would the information already be present? For example with dimension anomalies, depending on how you write it I find it difficult to believe that the data would already be in Elementary's tables. Maybe it would be there for volume anomalies?
• Assuming that Elementary is generally run as part of dbt test, but it uses a different target in profiles.yml than dbt test, how will it know which of the Elementary targets in profiles.yml to run?
• When I run Elementary locally and look at the test cases in dbt's target directory, I see a bunch of no-op tests like the following. Why would this be happening?

select
      count(*) as failures,
      count(*) != 0 as should_warn,
      count(*) != 0 as should_error
    from (
              
    with nothing as (select 1 as num)
    select * from nothing where num = 2


    ) dbt_internal_test

I can't find the answers to these questions documented anywhere.