test: add unit tests for Advent scheduler tracker file operations

Author: wiktoriavh

test/advent-scheduler.test.mjs

@@ -0,0 +1,67 @@
+import assert from 'node:assert/strict';
+import { promises as fs } from 'node:fs';
+import test from 'node:test';
+
+const TEST_TRACKER_FILE = 'test-advent-tracker.json';
+
+/**
+ * Helper function to load tracker data
+ */
+async function loadTracker(filename) {
+  try {
+    const data = await fs.readFile(filename, 'utf-8');
+    return JSON.parse(data);
+  } catch (error) {
+    return {};
+  }
+}
+
+/**
+ * Helper function to save tracker data
+ */
+async function saveTracker(filename, data) {
+  await fs.writeFile(filename, JSON.stringify(data, null, 2), 'utf-8');
+}
+
+/**
+ * Helper function to clean up test tracker file
+ */
+async function cleanupTestTracker() {
+  try {
+    await fs.unlink(TEST_TRACKER_FILE);
+  } catch (error) {
+    // File might not exist, that's fine
+  }
+}
+
+test('advent scheduler: tracker file operations', async (t) => {
+  await t.test('should create empty tracker if file does not exist', async () => {
+    await cleanupTestTracker();
+    const tracker = await loadTracker(TEST_TRACKER_FILE);
+    assert.deepEqual(tracker, {});
+  });
+
+  await t.test('should save and load tracker data correctly', async () => {
+    const testData = {
+      '2025': [1, 2, 3],
+      '2026': [1],
+    };
+    await saveTracker(TEST_TRACKER_FILE, testData);
+    const loaded = await loadTracker(TEST_TRACKER_FILE);
+    assert.deepEqual(loaded, testData);
+  });
+
+  await t.test('should track multiple days per year', async () => {
+    const tracker = {
+      '2025': [1, 5, 10, 15, 20, 25],
+    };
+    await saveTracker(TEST_TRACKER_FILE, tracker);
+    const loaded = await loadTracker(TEST_TRACKER_FILE);
+    assert.equal(loaded['2025'].length, 6);
+    assert.ok(loaded['2025'].includes(1));
+    assert.ok(loaded['2025'].includes(25));
+  });
+
+  // Cleanup
+  await cleanupTestTracker();
+});