test: add more chat completions cases

[bzp2010]

Summary by CodeRabbit

• Tests
  • Expanded chat-completions coverage for streaming parity, tool-calling (including parallel calls), usage-only chunks, trailing content after finish, multimodal content, and new response-format behaviors
• Tests / Utilities
  • Added richer SSE-aware stream assertions and summarization helpers plus a generator for trailing-content stream events to validate advanced streaming behavior

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 3555084f-ad7d-4741-9080-659038d69388

📥 Commits

Reviewing files that changed from the base of the PR and between 3327e8a and 44e87b2.

📒 Files selected for processing (1)

• tests/package.json

✅ Files skipped from review due to trivial changes (1)

• tests/package.json

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📝 Walkthrough

Walkthrough

This PR adds structured SSE frames to the mock upstream (per-frame event, delay, and disconnect), refactors stream assertions into a ChatCompletionStreamSummary model, and expands unit and end-to-end tests for streaming parity, trailing content, usage-only chunks, tool-call parsing, and OpenAI feature forwarding.

Changes

SSE Streaming Infrastructure and Test Coverage Expansion

Layer / File(s)	Summary
SSE Frame Types & Protocol tests/fixtures/mock-upstream.ts	Introduces OpenAiMockSseFrame interface with data, optional event, delayMs, and disconnectAfterWrite; updates OpenAiMockStreamEvent to accept structured frames or raw stream data.
SSE Rendering & Streaming Loop tests/fixtures/mock-upstream.ts	Adds SSE renderer to output event: headers (when present) and data: payloads; refactors streaming loop to normalize events into frames, support per-frame socket destruction, and apply per-frame delays.
Trailing Content Builder tests/fixtures/mock-upstream.ts	Adds buildOpenAiTrailingContentAfterFinishReasonStreamEvents helper generating a sequence with finish_reason stop, trailing delta, and [DONE] marker.
Stream Assertion Framework Refactor tests/utils/stream-assert.ts	Introduces ChatCompletionStreamSummary model with aggregated text, usage chunks, finish reasons, and tool calls; adds chatCompletionEvents parser and summarizeChatCompletionStream function; introduces expectStreamHasUsageOnlyChunk and expectStreamRetainsTrailingContentAfterFinishReason; refactors existing assertions to use summary data.
Re-exports & Test Imports tests/utils/mock-upstream.ts, tests/proxy/chat-completions.test.ts, tests/utils/stream-assert.test.ts	Expands re-exports to include buildOpenAiTrailingContentAfterFinishReasonStreamEvents and OpenAiMockSseFrame; updates test imports to include new stream assertion helpers.
Stream Assertion Unit Tests tests/utils/stream-assert.test.ts, tests/utils/mock-upstream.test.ts	Adds test for SSE body conversion; validates trailing content detection and usage-only chunk filtering; tests tool-call JSON argument parsing and aggregation; verifies scripted SSE streaming behavior with event/data markers.
Chat Completions End-to-End Coverage tests/proxy/chat-completions.test.ts	Adds 16 new tests covering streaming/non-stream parity, trailing content retention, usage-only streams, tool-call equivalence, response_format (json_schema/json_object), multimodal images, reasoning tokens, tool-choice variants (required/function form), and parallel tool calls.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• api7/aisix#31: Modifies mock upstream early-disconnect option; this PR refactors SSE events into structured frames with per-frame socket control, complementing the earlier disconnect model.
• api7/aisix#30: Extends mock upstream and stream-assert utilities for tool-call and SSE handling; this PR builds on that foundation with frame-based protocol and comprehensive assertion refactors.
• api7/aisix#29: Modifies mock upstream types and helpers; this PR introduces structured SSE frames and new trailing-content builder as a successor enhancement to the mock protocol.

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'test: add more chat completions cases' accurately summarizes the main changes: expanded test coverage for chat completions with new test cases, helper functions, and refactored assertion utilities.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
E2e Test Quality Review	✅ Passed	Excellent E2E tests: 33 cases with real service startup, comprehensive scenarios (auth, validation, streaming, tools), proper isolation, clear structured assertions.
Security Check	✅ Passed	No sensitive data exposure, credential leakage, authorization bypass, TLS errors, or security vulnerabilities detected. All API keys are test-only and properly scoped.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch bzp/test-chat-completions-more-cases

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