test(bigquery): add long-running heavy poller test

[haphungw]

Add an integration test that proves the JobPoller LRO backoff logic is invoked.

Typical testing queries (e.g., SELECT 1) execute so fast that the initial insert_job REST call fast-paths and returns DONE instantly. This suppresses the inner .poll() loop from back-off sleeping, leaving the LRO logic untested.

Follow-up to #6232

[gemini-code-assist]

Code Review

This pull request adds a new integration test, job_service_poller_heavy, to test the BigQuery job poller with a delayed query. Feedback was provided regarding the use of a tight busy loop in the BigQuery script, which can exceed the statement execution limit and cause test failures; using a temporary JavaScript UDF is recommended instead.

[gemini-code-assist]

Using a tight busy loop in BigQuery scripting (e.g., WHILE WAIT = 'TRUE' DO ...) will quickly exceed the BigQuery scripting limit of 1,000 executed statements per query, causing the test to fail with a Resources exceeded error.

To implement a reliable delay without hitting the statement limit, you can use a temporary JavaScript UDF that performs the busy-wait. This executes as a single statement in BigQuery.

    let query = r#"
        CREATE TEMP FUNCTION wait(ms INT64) RETURNS STRING LANGUAGE js AS '
          const start = Date.now();
          while (Date.now() - start < ms) {}
          return "done";
        ';
        SELECT wait(5000);
    "#;

[suzmue]

https://docs.cloud.google.com/bigquery/docs/reference/standard-sql/datetime_functions#current_datetime - Based on this, I think current datetime will not update over the course of the function so this will not work as expected

[haphungw]

Thank you, TIL. I borrowed this from the Python SDK 😢

To make the execution time deterministic, I think we can switch to a massive Cartesian cross-join (which is what the Go team does).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.18%. Comparing base (6f373a5) to head (4cf63e7).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6406      +/-   ##
==========================================
- Coverage   96.18%   96.18%   -0.01%     
==========================================
  Files         288      288              
  Lines       75424    75424              
==========================================
- Hits        72548    72547       -1     
- Misses       2876     2877       +1     

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