diff --git a/app/common/ValueCache.test.mjs b/app/common/ValueCache.test.mjs
new file mode 100644
index 0000000..8841a59
--- /dev/null
+++ b/app/common/ValueCache.test.mjs
@@ -0,0 +1,118 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+
+vi.mock('fs/promises', () => ({
+  default: {
+    readFile: vi.fn(),
+    writeFile: vi.fn(),
+    mkdir: vi.fn(),
+  },
+}));
+
+const fs = (await import('fs/promises')).default;
+
+const { default: ValueCache } = await import('./ValueCache.mjs');
+
+describe('ValueCache', () => {
+  let cache;
+
+  beforeEach(() => {
+    cache = new ValueCache('test-key');
+    vi.clearAllMocks();
+  });
+
+  describe('path', () => {
+    it('returns storage/cache/{key}.json', () => {
+      expect(cache.path).toBe('storage/cache/test-key.json');
+    });
+
+    it('uses the key from constructor', () => {
+      const other = new ValueCache('other');
+      expect(other.path).toBe('storage/cache/other.json');
+    });
+  });
+
+  describe('get', () => {
+    it('returns parsed JSON when valid and not expired', async () => {
+      const item = { data: 'hello', expires: Date.now() + 60000, cachedAt: new Date().toISOString() };
+      fs.readFile.mockResolvedValue(JSON.stringify(item));
+      const result = await cache.get();
+      expect(result).toEqual(item);
+    });
+
+    it('returns null when expired', async () => {
+      const item = { data: 'hello', expires: Date.now() - 60000, cachedAt: new Date().toISOString() };
+      fs.readFile.mockResolvedValue(JSON.stringify(item));
+      expect(await cache.get()).toBeNull();
+    });
+
+    it('returns item when no expiry is set', async () => {
+      const item = { data: 'hello', expires: null, cachedAt: new Date().toISOString() };
+      fs.readFile.mockResolvedValue(JSON.stringify(item));
+      const result = await cache.get();
+      expect(result).toEqual(item);
+    });
+
+    it('returns null when file is missing', async () => {
+      fs.readFile.mockRejectedValue(new Error('ENOENT'));
+      expect(await cache.get()).toBeNull();
+    });
+  });
+
+  describe('getData', () => {
+    it('returns .data field from cached item', async () => {
+      const item = { data: { foo: 'bar' }, expires: Date.now() + 60000, cachedAt: new Date().toISOString() };
+      fs.readFile.mockResolvedValue(JSON.stringify(item));
+      expect(await cache.getData()).toEqual({ foo: 'bar' });
+    });
+
+    it('returns null when no cache', async () => {
+      fs.readFile.mockRejectedValue(new Error('ENOENT'));
+      expect(await cache.getData()).toBeNull();
+    });
+  });
+
+  describe('getCachedAt', () => {
+    it('returns Date from cachedAt field', async () => {
+      const cachedAt = '2024-06-15T10:00:00.000Z';
+      const item = { data: 'x', cachedAt };
+      fs.readFile.mockResolvedValue(JSON.stringify(item));
+      const result = await cache.getCachedAt();
+      expect(result).toEqual(new Date(cachedAt));
+    });
+
+    it('returns null when no data', async () => {
+      fs.readFile.mockRejectedValue(new Error('ENOENT'));
+      expect(await cache.getCachedAt()).toBeNull();
+    });
+  });
+
+  describe('setData', () => {
+    it('writes JSON with data, expires, and cachedAt', async () => {
+      fs.mkdir.mockResolvedValue(undefined);
+      fs.writeFile.mockResolvedValue(undefined);
+
+      await cache.setData({ key: 'value' }, Date.now() + 60000);
+
+      expect(fs.mkdir).toHaveBeenCalledWith('storage/cache', { recursive: true });
+      expect(fs.writeFile).toHaveBeenCalledWith(
+        'storage/cache/test-key.json',
+        expect.stringContaining('"key": "value"'),
+      );
+
+      const written = JSON.parse(fs.writeFile.mock.calls[0][1]);
+      expect(written.data).toEqual({ key: 'value' });
+      expect(written.expires).toBeDefined();
+      expect(written.cachedAt).toBeDefined();
+    });
+
+    it('passes null expires when not specified', async () => {
+      fs.mkdir.mockResolvedValue(undefined);
+      fs.writeFile.mockResolvedValue(undefined);
+
+      await cache.setData('test');
+
+      const written = JSON.parse(fs.writeFile.mock.calls[0][1]);
+      expect(written.expires).toBeNull();
+    });
+  });
+});
diff --git a/app/common/fs.test.mjs b/app/common/fs.test.mjs
new file mode 100644
index 0000000..b01fc8e
--- /dev/null
+++ b/app/common/fs.test.mjs
@@ -0,0 +1,49 @@
+import { describe, it, expect, vi } from 'vitest';
+import { mkdirp, exists, olderThan } from './fs.mjs';
+
+vi.mock('fs/promises', () => ({
+  default: {
+    mkdir: vi.fn(),
+    access: vi.fn(),
+    stat: vi.fn(),
+  },
+}));
+
+const fs = (await import('fs/promises')).default;
+
+describe('mkdirp', () => {
+  it('calls fs.mkdir with recursive: true', async () => {
+    fs.mkdir.mockResolvedValue(undefined);
+    await mkdirp('/some/path');
+    expect(fs.mkdir).toHaveBeenCalledWith('/some/path', { recursive: true });
+  });
+});
+
+describe('exists', () => {
+  it('returns true when fs.access succeeds', async () => {
+    fs.access.mockResolvedValue(undefined);
+    expect(await exists('/some/file')).toBe(true);
+  });
+
+  it('returns false when fs.access throws', async () => {
+    fs.access.mockRejectedValue(new Error('ENOENT'));
+    expect(await exists('/missing/file')).toBe(false);
+  });
+});
+
+describe('olderThan', () => {
+  it('returns true when mtime is before cutoff', async () => {
+    fs.stat.mockResolvedValue({ mtime: new Date('2024-01-01') });
+    expect(await olderThan('/file', new Date('2024-06-01'))).toBe(true);
+  });
+
+  it('returns false when mtime is after cutoff', async () => {
+    fs.stat.mockResolvedValue({ mtime: new Date('2024-06-01') });
+    expect(await olderThan('/file', new Date('2024-01-01'))).toBe(false);
+  });
+
+  it('returns true when file is missing', async () => {
+    fs.stat.mockRejectedValue(new Error('ENOENT'));
+    expect(await olderThan('/missing', new Date())).toBe(true);
+  });
+});