TestGen Agent

The TestGen agent receives error detection messages and generates bun:test reproduction tests to confirm that a bug exists.

Responsibilities

• Generate TypeScript test files from error context using LLM
• Execute tests in isolated Sandbox containers
• Confirm reproduction (test must fail to prove the bug)
• Store artifacts in R2 and publish to the triage-ready queue

How It Works

Test Generation

1. Receive an ErrorDetectedMessage from the queue
2. Fetch the service config to get the repository URL
3. Build a prompt with the sample event: route, status code, error message, stack trace
4. Call Workers AI to generate a bun:test file
5. If the LLM output doesn’t contain valid bun:test imports, use a fallback template

Sandbox Execution

If a Sandbox binding and repository URL are available:

1. Clone the repository in the Sandbox container
2. Install dependencies (bun install)
3. Write the generated test file
4. Execute the test

Reproduction is confirmed when the test fails — this proves the error can be reproduced in the codebase.

Artifacts

Three artifacts are stored in R2 for each incident:

File	Description
test-case.ts	The generated reproduction test
test-result.json	{ reproductionConfirmed, generatedAt }
sample-event.json	The original observability event

Failure Handling

If the test passes (bug not reproduced), the incident is marked needs_human. A human developer should investigate whether the test generation was faulty or if the error is transient.

HTTP Endpoints

Method	Path	Description
POST	/generate	Generate a test case from an error message
GET	/status	Current agent state

Source

src/agents/test-gen.ts