Add Jest testing framework and initial test cases for issues called out in #181

- Created jest.config.js for Jest configuration.
- Updated package.json to include Jest and TypeScript types for Jest.
- Added test scripts for running tests and coverage.
- Implemented initial unit tests for icalUtils functions and recurring events.
- Enhanced README with testing instructions and guidelines for adding new tests.
- Fixed bug caused by non-existent .last / .first

Author: muness

README.md

@@ -139,3 +139,17 @@ If for some reason you want to install the plugin manually:
 4. `npm run dev` will watch for changes and build the plugin to `dist/main.js`.
 5. copy the `dist/main.js` (or `dist/main-debug.js` if you want the un-minified version) to your Obdisian vault plugin folder (`cp dist/main.js <vault>/.obsidian/plugins/ics/main.js`).
 6. Reload the vault or use the [Hot Reload Plugin](https://github.com/pjeby/hot-reload).
+
+### Testing
+
+The plugin includes a test harness for recurring events and timezone handling to prevent regressions:
+
+```bash
+# Run all tests
+npm test
+
+# Run tests in watch mode (automatically re-runs when files change)
+npm run test:watch
+```
+
+See `tests/README.md` for information about how to add new tests.

jest.config.js

@@ -0,0 +1,18 @@
+module.exports = {
+  preset: 'ts-jest',
+  testEnvironment: 'node',
+  roots: ['<rootDir>/src', '<rootDir>/tests'],
+  testMatch: [
+    '**/__tests__/**/*.ts',
+    '**/?(*.)+(spec|test).ts'
+  ],
+  transform: {
+    '^.+\\.ts$': 'ts-jest',
+  },
+  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node'],
+  collectCoverageFrom: [
+    'src/**/*.ts',
+    '!src/**/*.d.ts',
+  ],
+  setupFilesAfterEnv: ['<rootDir>/tests/setup.ts']
+};