Automatic jest test generation for GitHub PRs with dual AI review

Workflow: Automatic Unit Test Creator from GitHub

🏗️ Architecture Overview

This workflow listens for GitHub pull-request events, analyzes changed React/TypeScript files, auto-generates Jest tests via AI, has them reviewed by a second AI pass, and posts suggestions back as PR comments:

1. GitHub Webhook → PR opened or updated
2. Fetch & Diff → Retrieve raw diff of changed files
3. Filter & Split → Isolate .tsx files & their diffs
4. Fetch File Contents → Provide full context for tests
5. Test Maker Agent → Generate Jest tests for diff hunks
6. Code Reviewer Agent → Refine tests for style & edge-cases
7. Post PR Comment → Sends suggested tests back to GitHub

📦 Node-by-Node Breakdown

flowchart LR
  A[Webhook: /github/pr-events] --> B[GitHub: Get PR]
  B --> C[Function: Parse diff_url + owner/repo]
  C --> D[HTTP Request: GET diff_url]
  D --> E[Function: Split on "diff --git"]
  E --> F[Filter: /\.tsx$/]
  F --> G[GitHub: Get File Contents]
  G --> H[Test Maker Agent]
  H --> I[Code Reviewer Agent]
  I --> J[Function: Build Comment Payload]
  J --> K[HTTP Request: POST to PR Comments]

Webhook: GitHub PR Events

• Type: HTTP Webhook (/webhook/github/pr-events)
• Subscribed Events: pull_request.opened, pull_request.synchronize

GitHub: Get PR

• Node: GitHub
• Action: "Get Pull Request"
• Inputs: owner, repo, pull_number

Function: Parse diff_url + owner/repo

• Extracts:
  • diff_url (e.g. …/pulls/123.diff)
  • owner, repo, merge_commit_sha

HTTP Request: GET diff_url

• Fetches unified-diff text for the PR.

Function: Split on "diff --git"

• Splits the diff into file-specific segments.

Filter: /.tsx$/

• Keeps only segments where the file path ends with .tsx.

GitHub: Get File Contents

• For each .tsx file, fetches the latest blob via GitHub API.

Test Maker Agent

• Prompt:
  • "Generate Jest unit tests covering only the behaviors changed in these diff hunks."
• Output: Raw Jest test code.

Code Reviewer Agent

• Reads file + generated tests
• Prompt:
  • "Review and improve these tests for readability, edge-cases, and naming conventions."
• Output: Polished test suite.

Function: Build Comment Payload

• Wraps tests in TypeScript fences:

// generated tests…

• Constructs JSON:

{ "body": "<tests>" }

HTTP Request: POST to PR Comments

• URL: https://api.github.com/repos/{owner}/{repo}/issues/{pull_number}/comments
• Body: Contains the suggested tests.

🔍 Design Rationale & Best Practices

Focused Diff Analysis

• Targets only .tsx files to cover UI logic.

Two-Stage AI

• Separate "generate" + "review" steps mimic TDD + code review.

Stateless Functions

• Pure JS for parsing & transformation, easy to test.

Non-Blocking PR Comments

• Asynchronous suggestions—developers aren't blocked.

Scoped Permissions

• GitHub token limited to reading PRs & posting comments.