Setup CI workflow and testing environment

.github/workflows/ci.yml

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+name: Build and Test
+
+on:
+  push:
+    branches:
+      - main
+      - master
+  pull_request:
+    branches:
+      - main
+      - master
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: "16"
+          cache: "npm"
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Create .env
+        run: cp example.env .env
+
+      - name: Build
+        run: npm run build
+
+      - name: Test
+        run: npm test

docs/TESTING.md

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+# Testing Strategy
+
+This project uses [Jest](https://jestjs.io/) for testing. Since the code runs in the Google Apps Script (GAS) environment, we use a combination of unit tests for pure logic and integration tests with mocked GAS globals.
+
+## Running Tests
+
+To run the tests, execute:
+
+```bash
+npm test
+```
+
+This will run all files ending in `.test.ts`.
+
+## Unit Tests
+
+Unit tests are located in `src/lib/*.test.ts` (or alongside the file they test). They focus on pure functions that do not depend on `SpreadsheetApp`, `GmailApp`, etc.
+
+**Example:** `src/lib/utils.test.ts` tests `sanitize` and `proposeEmail` functions.
+
+## Integration Tests & Mocking
+
+Integration tests simulate the execution of handlers (like `onFormSubmit`) by mocking the global objects provided by Google Apps Script.
+
+### Mocks Location
+
+Mocks are defined in `tests/mocks/google-apps-script.ts`. This file exports objects like `SpreadsheetApp`, `GmailApp`, `HtmlService`, etc., with Jest mock functions.
+
+### How to Write a New Integration Test
+
+1.  **Import the Mocks:**
+    Import the mock setup *before* importing your handler. This ensures that when your handler is imported, the global variables are already available.
+
+    ```typescript
+    import "../../tests/mocks/google-apps-script";
+    import { yourHandler } from "./yourHandler";
+    import { SpreadsheetApp, GmailApp } from "../../tests/mocks/google-apps-script";
+    ```
+
+2.  **Reset Mocks:**
+    Use `beforeEach` to clear mocks and set up specific return values for your test case.
+
+    ```typescript
+    beforeEach(() => {
+      jest.clearAllMocks();
+      // Setup specific behavior
+      (SpreadsheetApp.getActiveSpreadsheet as jest.Mock).mockReturnValue(...);
+    });
+    ```
+
+3.  **Mock Complex Interactions:**
+    For chained calls like `sheet.getRange(row, col).getValue()`, you may need to implement a mock function that returns an object with its own mocked methods. See `src/handlers/formHandler.test.ts` for a comprehensive example.
+
+4.  **Assertions:**
+    Use Jest's `expect` to verify that side effects occurred as expected (e.g., `setValue` was called on a specific cell, or `GmailApp.sendEmail` was triggered).
+
+    ```typescript
+    expect(mockRange.setValue).toHaveBeenCalledWith("expected value");
+    ```
+
+## CI/CD
+
+Tests are automatically run on every Push and Pull Request to the `main` or `master` branch via GitHub Actions (`.github/workflows/ci.yml`).

jest.config.js

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+module.exports = {
+  preset: "ts-jest",
+  testEnvironment: "node",
+  testMatch: ["**/*.test.ts"],
+  transform: {
+    "^.+\\.tsx?$": [
+      "ts-jest",
+      {
+        diagnostics: false,
+      },
+    ],
+  },
+};