Add test suite for Big presentation library

.github/workflows/test.yml

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+name: Tests
+
+on:
+  push:
+    branches: [ main, master ]
+  pull_request:
+    branches: [ main, master ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    permissions:
+      contents: read
+
+    strategy:
+      matrix:
+        node-version: [18.x, 20.x]
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Use Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v4
+      with:
+        node-version: ${{ matrix.node-version }}
+        cache: 'npm'
+
+    - name: Install dependencies
+      run: npm ci
+
+    - name: Run tests
+      run: npm test
+
+    - name: Generate coverage report
+      run: npm run test:coverage

.gitignore

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+node_modules/
+coverage/
+.DS_Store
+*.log

README.md

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 # Big
 
+[![Tests](https://github.com/sroberts/big/actions/workflows/test.yml/badge.svg)](https://github.com/sroberts/big/actions/workflows/test.yml)
+
 <p align="center">
   <img width="540" src='.github/logo.png' />
 </p>

TEST_README.md

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+# Big Presentation Library - Test Suite
+
+This directory contains tests for the Big presentation library.
+
+## Running Tests
+
+To run the test suite:
+
+```bash
+npm test
+```
+
+To run tests in watch mode:
+
+```bash
+npm run test:watch
+```
+
+To generate a coverage report:
+
+```bash
+npm run test:coverage
+```
+
+## Test Structure
+
+The test suite is organized into the following sections:
+
+### 1. Utility Functions
+Tests for the core utility functions used internally by Big:
+- `emptyNode()` - Removes all child nodes from an element
+- `ce()` - Creates elements with class names
+- `parseHash()` - Extracts slide numbers from URL hashes
+
+### 2. Integration Tests
+Integration tests that verify the library's behavior in a browser-like environment. These tests are currently skipped because jsdom doesn't fully support the dynamic `window.location` behavior that big.js requires.
+
+For full integration testing in a real browser environment, consider using:
+- [Puppeteer](https://pptr.dev/)
+- [Playwright](https://playwright.dev/)
+- [Cypress](https://www.cypress.io/)
+
+### 3. Exported API
+Tests that verify the library exports the correct API surface:
+- Event listeners (load, keyboard, click, touch)
+- `window.big` object
+- Presentation modes (talk, print, jump)
+- Speaker notes handling
+
+### 4. CSS Integration
+Tests that verify the CSS file exists and contains the required styles.
+
+### 5. HTML Template
+Tests that verify the HTML template exists and has the correct structure.
+
+## Test Coverage
+
+The test suite covers:
+- ✅ Core utility functions
+- ✅ API surface validation
+- ✅ Event handler presence
+- ✅ File existence and structure
+- ⏭️ Runtime integration behavior (skipped due to jsdom limitations)
+
+## Dependencies
+
+The test suite uses:
+- **Jest** - Test framework
+- **jsdom** - Browser environment simulation
+- **@testing-library/dom** - DOM testing utilities
+- **@testing-library/jest-dom** - Custom Jest matchers
+
+## Notes
+
+The integration tests that exercise the full runtime behavior of Big are skipped because jsdom (the DOM implementation used by Jest) doesn't fully support all browser features that Big relies on, particularly around `window.location.hash` manipulation.
+
+For comprehensive end-to-end testing, it's recommended to use a real browser automation tool like Puppeteer or Playwright in addition to these unit tests.