[chikamura]

Summary

Adds a MockWebServer-based test suite (TestBigqueryClientWithMockServer, TestBigqueryJavaOutputPluginWithMockServer) for BigqueryClient and BigqueryJavaOutputPlugin. To let ./gradlew test verify behavior without talking to the real BigQuery API, adds a way for BigqueryClient to connect to a test server, along with a new utility class for it, BigqueryTestHostSupport.java.

• Adds a test_host config option. It only takes effect when the TEST_HOST_ENABLED environment variable is also set, which in practice only happens under ./gradlew test.
  • test_host is used for all of BigqueryClient's BigQuery API calls.
  • test_host also overrides load()'s behavior: google-cloud-bigquery:2.14.0 ignores test_host (BigQueryOptions#setHost()) for one of load()'s connections and hardcodes it to https://www.googleapis.com, so this override works around that.
• Adds TestBigqueryClientWithMockServer and TestBigqueryJavaOutputPluginWithMockServer, covering:
  • Retry/give-up behavior for load, copy, query, merge, and createTableIfNotExist jobs
  • updateTableIfNeed()'s interaction between mode, retain_column_descriptions/retain_column_policy_tags, and column_options[].description
  • An end-to-end run per mode (append, append_direct, replace, delete_in_advance, merge) against a mocked BigQuery API
• Adds a com.squareup.okhttp3:mockwebserver:4.11.0 dependency and environment "TEST_HOST_ENABLED", "true" to the test task in build.gradle.

Not in scope

Several known Ruby-vs-Java behavior differences are documented as TODO comments in the new tests (not fixed here):

• column_options[].description only applies to mode: replace in Java, whereas Ruby applies it regardless of mode
• The plugin's retries config is only consulted by the job-polling loops (load/copy/query); it has no effect on other API calls such as createTableIfNotExist(), getTable(), deleteTable(), createDataset(), or updateTableIfNeed()'s PATCH — those rely on the underlying BigQuery client library's own default retry behavior instead
• If the load, copy, or merge job itself fails after exhausting retries (e.g. an API error), the run aborts before ever reaching the temp table delete step, leaving the temp table behind
• A failed temp-table delete blocks the schema update that would otherwise follow it
• A partition decorator in the table name is passed straight through to createTableIfNotExist() (Ruby strips it)

This PR is test coverage only; those are left as follow-ups.

Test plan

• ./gradlew test — 104 tests pass
• ./gradlew spotlessApply

[john-abre]

ありがとうございます！＆非常に遅くなって申し訳無かったです 🙇

• 必須じゃないですがテーブルのない時のdelete_in_advance動作確認したければ #121 おまけ用意してみました 🙇

• テストは「今の状態」の確認で、PRによってRubyっぽくなる時は更新の必要性は承知です 🙇 （具体的にPR1, PR3, PR4, PR5, PR6に合わせる更新が期待）

メモ for 個人理解：

• BigqueryTestHostSupport creates BigQueryOptions that send BigQuery requests to mock server
• It also provides a “createLoadJob()” which is used inside of load() to make jobs.insert POST (to mock server) rather than calling Google servers