Test IPv6 and dual-stack entrypoints

[dkropachev]

Jira: DRIVER-823

Cover IPv6 and dual-stack entrypoint behavior in the Node transport:

• exercise discovery and DynamoDB routing through a literal IPv6 seed
• cover deterministic A-only and AAAA-only DNS entrypoints
• cover failed-AAAA-to-A and failed-A-to-AAAA fallback
• verify an all-unavailable dual-stack endpoint returns promptly and preserves the configured seed
• assert IPv6 URL and Host header bracket formatting

The existing implementation already preserves DNS hostnames, replaces seeds with learned nodes after discovery, and retains configured seeds as discovery recovery candidates.

Verification: npm run verify (62 tests passed).

[Copilot]

🟡 Changes recommended

Timing and fresh-connection fallback behavior are not fully verified.

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Pull request overview

Adds Node transport coverage for IPv6 and dual-stack entrypoints.

Changes:

• Tests IPv6 discovery, routing, URL, and Host formatting.
• Tests DNS family selection, fallback, and seed retention.

File summaries

File	Description
test/discovery.test.ts	Adds IPv6 and dual-stack transport tests and DNS lookup helper.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 2
• Review effort level: Balanced

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[Copilot]

🟢 Ready to approve

The focused test additions correctly cover the described transport behavior without production-code risk.

This review doesn't count toward merge requirements. Sign up for the private preview to control whether Copilot approvals count.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0 new
• Review effort level: Balanced

We're testing this review assessment. Please use 👍 or 👎 to tell us if it's correct.