Overhaul testing framework

.github/workflows/ci.yml

@@ -11,10 +11,11 @@ jobs:
       - name: Use Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: '16'
           cache: 'npm'
       - name: Install dependencies
         run: npm install
+      - name: Install browsers
+        run: npx playwright install --with-deps
       - name: Run tests
-        run: npm test
+        run: npm run ci
 

.gitignore

@@ -1,2 +1,3 @@
 /node_modules/
-.idea
+/coverage
+.idea

TESTING.md

@@ -0,0 +1,53 @@
+# Idiomorph Testing Guide
+
+This guide outlines how to test Idiomorph, focusing on running tests headlessly or in a browser environment, running individual tests, and other testing concerns.
+
+## Prerequisites
+
+1. Ensure you have a currently supported Node.js and npm installed.
+2. Install dependencies by running:
+   ```bash
+   npm install
+   npx playwright install
+   ```
+
+## Running All Tests
+
+To run all tests in headless mode, execute:
+```bash
+npm test
+```
+This will run all the tests using headless Chrome.
+
+To run all tests against all browsers in headless mode, execute:
+```bash
+npm run ci
+```
+This will run the tests using Playwright’s headless browser setup across Chrome, Firefox, and WebKit (Safari-adjacent). This is ultimately what gets run in Github Actions to verify PRs.
+
+## Running Individual Tests
+
+### Headless Mode
+To run a specific test file headlessly, for example `test/core.js`, use the following command:
+```bash
+npm test test/core.js
+```
+If you want to run only one specific test, you can temporarily change `it("...` to `it.only("...` in the test file, and then specify the test file as above. Don't forget to undo this before you commit!
+
+### Headed Mode (Interactive Browser Tests)
+To run tests in a non-headless mode (with a visible browser window):
+```bash
+npm run debug
+```
+This will start the server, and open the test runner in a browser. From there you can choose a test file to run.
+
+## Code Coverage Report
+After a test run completes, you can open `coverage/lcov-report/index.html` to view the code coverage report. On Ubuntu you can run:
+```bash
+xdg-open coverage/lcov-report/index.html
+```
+
+## Test Locations
+- All tests are located in the `test/` directory. Only .js files in this directory will be discovered by the test runner, so support files can go in subdirectories.
+- The `web-test-runner.config.mjs` file in the root directory contains the boilerplate HTML for the test runs, including `<script>` tags for the test dependencies.
+