fix(test): resolve flag duplication in emulator tests, update GetObject count, and rename proxy log prefix

[alleaditya]

Description

This PR resolves a test isolation issue in the gcsfuse emulator integration tests:

1. Flag Accumulation Bug: In grpc_header_validation_test.go and writes_stall_on_sync_test.go, flags were being appended in-place to a suite-level or loop-level slice. Since the test instances are reused across multiple sub-tests, this caused flags (specifically --custom-endpoint and --anonymous-access) to accumulate, leading to mounting errors (connecting to dead ports of previous test runs). This PR fixes it by copying the base flags before appending local test-specific flags.
2. Emulator GetObject Count: Updated the expected GetObject call count in TestGRPCHeadersInMultipleOperations from 3 to 4. This is because the test runs with gRPC enabled, which triggers a DirectPath verification call (gcsfuse-dp-object Stat) during mount that was previously not accounted for in the strict count assertion.
3. Kokoro Proxy Logs Collection: Renamed the proxy server log file prefix from proxy-server-failed- to gcsfuse-failed-integration-test-logs-proxy-server- to match the Kokoro artifact collection pattern in presubmit.cfg, ensuring proxy logs are successfully uploaded to GCS on failures.

Link to the issue in case of a bug fix.

NA

Testing details

1. Manual - NA
2. Unit tests - NA
3. Integration tests - Verified that emulator tests pass locally and checks are passing on Kokoro.

Any backward incompatible change? If so, please explain.

No.

[gemini-code-assist]

Summary of Changes

Hello, 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 improves the reliability and consistency of integration tests by addressing flag duplication issues and standardizing log file naming. It also updates specific test expectations to reflect current behavior, ensuring that validation logic remains accurate as test scenarios evolve.

Highlights

• Flag Management: Implemented base flag preservation in emulator tests to prevent duplicate flag accumulation during test execution.
• Test Assertions: Updated the expected GetObject call count in GRPC header validation tests to account for additional verification steps.
• Logging: Renamed the proxy server log file prefix to improve consistency with existing GCSFuse log naming conventions.

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[gemini-code-assist]

Code Review

This pull request improves test isolation and reliability by ensuring that flag slices are correctly copied and reset between tests, preventing side effects from shared state. It also updates the proxy server log file prefix for better consistency. The reviewer suggested using GreaterOrEqual instead of an exact Equal assertion for RPC counts in TestGRPCHeadersInMultipleOperations to avoid test flakiness caused by asynchronous background operations.

[gemini-code-assist]

Following the general rules for this repository, assertions on RPC counts should use GreaterOrEqual instead of Equal when asynchronous background tasks (like metadata prefetch) might trigger additional calls. This helps prevent test flakiness due to non-deterministic timing of these async operations.

Suggested change

	assert.Equal(g.T(), 4, strings.Count(logStr, "/google.storage.v2.Storage/GetObject"), "Expected 4 GetObject calls (1 verification + 3 operations)")
	assert.GreaterOrEqual(g.T(), strings.Count(logStr, "/google.storage.v2.Storage/GetObject"), 4, "Expected at least 4 GetObject calls (1 verification + 3 operations)")

References

1. When asserting the count of operations in tests where asynchronous background tasks (such as metadata prefetch) might trigger additional calls, use 'GreaterOrEqual' instead of exact 'Equal' assertions if the precise count is already verified in other dedicated test cases. This approach helps prevent test flakiness due to non-deterministic timing of async operations.