Short answer
Use Copilot interactively to speed local test writing, and if you need fully automated test generation on PRs use an LLM-based CI job (ChatGPT/OpenAI or similar) with strict guardrails. Copilot itself is primarily an IDE assistant—not a production CI API—so mix interactive use + CI automation for safe, scalable results.
Recommendation
Start by surfacing Copilot suggestions to developers (VS Code/JetBrains) so PRs contain AI-written tests that humans review. For fully automated generation in GitHub Actions, use a dedicated LLM API in a separate job that creates a draft branch/PR with generated tests, then run the normal test matrix and require human review before merge.
Decision criteria (pick path by your constraints)
- Budget: LLM API in CI costs money per generation; Copilot interactive is included in developer licenses.
- Skill level: Automated CI generation needs engineering to add guardrails and secure secrets; interactive Copilot needs only IDE setup.
- Team size / workflow stage: Small teams or early-stage projects — start interactive. Large teams or high-volume PRs — consider automated generation with strict gates.
- Output quality / trust: If you need high-quality, well-reviewed tests, prefer human-in-the-loop Copilot. For scaling low-risk or boilerplate tests, automation can work.
Practical checklist to implement (two paths)
A. Interactive Copilot + CI test run (recommended first step)
1. Enable GitHub Copilot for devs; add guidelines and test templates in repo (naming, fixtures, mocks).
2. Developers accept Copilot suggestions and add tests in feature branches.
3. Standard GitHub Actions runs unit tests on PR opens/updates; require code owner review and CI passing before merge.
4. Add linter/action to detect AI-generated code metadata or add PR label (e.g., ai-generated) for reviewer attention.
B. Automated LLM-based test generation in GitHub Actions (when you need automation)
1. Choose LLM API (OpenAI/GPT or internal model). Note: Copilot doesn’t expose a CI API—use ChatGPT/OpenAI if you need programmatic access.
2. Create a workflow triggered on pull_request that: checks out code, invokes LLM with a constrained prompt (test template + relevant files), writes tests to a new branch, opens a draft PR via actions/github-script.
3. Run your test matrix on that draft PR. If tests pass, notify reviewers and require human sign-off to merge.
4. Add safety: sandbox network, no secrets exposed, static analysis for injected code, limit token/context, record prompt and responses, cache outputs to avoid re-generating.
Best-for / Avoid-if
- Best for: Quickly filling boilerplate tests, improving coverage for simple modules, accelerating individual devs with Copilot.
- Avoid if: Code interacts with sensitive systems, has high security needs, or requires deep domain understanding without review.
Extra practical tips
- Enforce review: always require human reviewer before merge. Treat generated tests as draft artifacts. Use coverage thresholds and flaky-test detection in CI.
- Monitor drift: add analytics (who/what generated tests) and periodically retrain internal test templates.
If you want, I can sketch a GitHub Actions workflow for the automated LLM path or a Copilot-based developer guide for your repo.
Compare GitHub Copilot and Cursor