Add unit tests for BigQuery to SQL transfer base operator

[desusaiteja]

Adds a dedicated unit test module for airflow.providers.google.cloud.transfers.bigquery_to_sql, which previously had no tests of its own — it is one of the missing provider test modules tracked in #35442.

The new providers/google/tests/unit/google/cloud/transfers/test_bigquery_to_sql.py covers the abstract BigQueryToSqlBaseOperator (the base for the BigQuery→MySQL/Postgres/MsSQL transfer operators) through a minimal concrete subclass:

• dataset_table parsing into dataset_id/table_id, including the ValueError for malformed values
• BigQueryHook construction with the operator's gcp_conn_id, location, and impersonation_chain
• execute() fetching from BigQuery and inserting every batch into the target SQL table with the right target_fields, replace, and commit_every arguments
• persist_links() being invoked with the task context
• get_openlineage_facets_on_complete() returning empty lineage when the BigQuery table cannot be fetched or the SQL hook provides no database info (the happy paths are already covered by the concrete operators' tests)

All 9 new tests pass locally, along with the existing bigquery_to_mysql/postgres/mssql test modules and the fast/manual prek static checks.

related: #35442

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Was generative AI tooling used to co-author this PR?

• Yes — Claude Code (Fable 5)

Generated-by: Claude Code (Fable 5) following the guidelines

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Important

🛠️ Maintainer triage note for @desusaiteja · by @potiuk · 2026-07-15 16:00 UTC

Helpful heads-up from the maintainers — please address before this PR can be reviewed (see our Pull Request quality criteria):

• ❌ Provider tests. See docs.

The ball is in your court — you've been assigned to this PR. Fix the above, then mark it Ready for review.

_{Automated triage — may be imperfect; a maintainer takes the next look.}