tests(google-cloud-bigquery-storage): drop usage of pytz in tests/*.py

[parthea]

This PR resolves the following failure which appears in

==================================== ERRORS ====================================
________________ ERROR collecting tests/unit/test_reader_v1.py _________________
ImportError while importing test module '/tmpfs/src/github/google-cloud-python/packages/google-cloud-bigquery-storage/tests/unit/test_reader_v1.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/usr/local/lib/python3.14/importlib/__init__.py:88: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
tests/unit/test_reader_v1.py:31: in 
    from .helpers import SCALAR_BLOCKS, SCALAR_COLUMN_NAMES, SCALAR_COLUMNS
tests/unit/helpers.py:20: in 
    import pytz
E   ModuleNotFoundError: No module named 'pytz'
_____________ ERROR collecting tests/unit/test_reader_v1_arrow.py ______________
ImportError while importing test module '/tmpfs/src/github/google-cloud-python/packages/google-cloud-bigquery-storage/tests/unit/test_reader_v1_arrow.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/usr/local/lib/python3.14/importlib/__init__.py:88: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
tests/unit/test_reader_v1_arrow.py:33: in 
    from .helpers import SCALAR_BLOCKS, SCALAR_COLUMN_NAMES, SCALAR_COLUMNS
tests/unit/helpers.py:20: in 
    import pytz
E   ModuleNotFoundError: No module named 'pytz'

pytz was used in tests but not explicitly installed. This PR removes usage of pytz in tests, although it is still needed transitively via pandas

[gemini-code-assist]

Summary of Changes

Hello @parthea, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the test suite for the google-cloud-bigquery-storage library to eliminate direct reliance on the pytz library for timezone handling. Instead, it leverages the built-in datetime.timezone.utc for defining UTC timezones in tests. This change modernizes the codebase by utilizing standard library features and streamlines test dependencies, while ensuring pytz remains available as an indirect dependency for pandas where required.

Highlights

• Test Modernization: The direct usage of the pytz library for timezone handling in system and unit tests has been removed, opting instead for the standard library's datetime.timezone.utc.
• Dependency Management: Unnecessary test dependencies cachetools and cryptography were removed from noxfile.py. pytz was explicitly added as a dependency in generator-input and constraints-3.7.txt to ensure pandas functionality, which may rely on pytz.
• Metadata Update: The last_generated_commit for google-cloud-bigquery-storage in .librarian/state.yaml was updated, likely reflecting a regeneration of client library configurations.

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[gemini-code-assist]

Code Review

This pull request effectively removes the direct dependency on pytz in the test suite by migrating to the standard library's datetime.timezone.utc. This is a great improvement for modernizing the codebase. I've added a few suggestions regarding dependency management best practices: pinning the version of the newly added pytz dependency for reproducibility, and keeping pull requests focused on a single concern. Overall, the changes are in a good direction.

[gemini-code-assist]

To ensure reproducible builds, it's a good practice to pin dependency versions. Please specify a version for pytz. For example, pytz==2023.3.

      pytz==2023.3

[gemini-code-assist]

This dependency removal is out of scope for this PR, which focuses on pytz. To maintain a clean and atomic commit history, it's best to handle unrelated changes in separate pull requests.

[gemini-code-assist]

Similar to the cachetools removal, this change is out of scope for this PR. Please group related changes into a single PR and keep unrelated changes separate for better reviewability and a cleaner commit history.

[gemini-code-assist]

For reproducible test runs, it's a good practice to pin all dependencies in a constraints file. Please add a specific version for pytz. For example, pytz==2023.3.

pytz==2023.3