diff --git a/frontend/lib/generateICS.test.ts b/frontend/lib/generateICS.test.ts
new file mode 100644
index 00000000..9e9f085a
--- /dev/null
+++ b/frontend/lib/generateICS.test.ts
@@ -0,0 +1,148 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { generateICS, downloadICS } from './generateICS';
+
+describe('generateICS', () => {
+  it('produces valid ICS envelope', () => {
+    const ics = generateICS([]);
+    expect(ics).toContain('BEGIN:VCALENDAR');
+    expect(ics).toContain('END:VCALENDAR');
+    expect(ics).toContain('VERSION:2.0');
+    expect(ics).toContain('PRODID:-//AgenticPay//Calendar Export//EN');
+  });
+
+  it('generates a VEVENT for each event', () => {
+    const ics = generateICS([
+      { uid: 'evt-1@test', summary: 'Milestone A', start: new Date('2026-01-15T00:00:00Z') },
+      { uid: 'evt-2@test', summary: 'Milestone B', start: new Date('2026-02-01T00:00:00Z') },
+    ]);
+    const beginCount = (ics.match(/BEGIN:VEVENT/g) ?? []).length;
+    const endCount = (ics.match(/END:VEVENT/g) ?? []).length;
+    expect(beginCount).toBe(2);
+    expect(endCount).toBe(2);
+  });
+
+  it('includes UID, SUMMARY, DTSTART, DTEND in each event', () => {
+    const ics = generateICS([
+      { uid: 'u1@ap', summary: 'Test Event', start: new Date('2026-03-10T00:00:00Z') },
+    ]);
+    expect(ics).toContain('UID:u1@ap');
+    expect(ics).toContain('SUMMARY:Test Event');
+    expect(ics).toContain('DTSTART:20260310T000000Z');
+    // default end = start + 1 day
+    expect(ics).toContain('DTEND:20260311T000000Z');
+  });
+
+  it('uses provided end date when supplied', () => {
+    const ics = generateICS([
+      {
+        uid: 'u2@ap',
+        summary: 'Ranged Event',
+        start: new Date('2026-04-01T00:00:00Z'),
+        end: new Date('2026-04-03T00:00:00Z'),
+      },
+    ]);
+    expect(ics).toContain('DTEND:20260403T000000Z');
+  });
+
+  it('includes DESCRIPTION when provided', () => {
+    const ics = generateICS([
+      {
+        uid: 'u3@ap',
+        summary: 'With Desc',
+        start: new Date('2026-05-01T00:00:00Z'),
+        description: 'Some details here',
+      },
+    ]);
+    expect(ics).toContain('DESCRIPTION:Some details here');
+  });
+
+  it('omits DESCRIPTION when not provided', () => {
+    const ics = generateICS([
+      { uid: 'u4@ap', summary: 'No Desc', start: new Date('2026-05-01T00:00:00Z') },
+    ]);
+    expect(ics).not.toContain('DESCRIPTION:');
+  });
+
+  it('escapes newlines in description', () => {
+    const ics = generateICS([
+      {
+        uid: 'u5@ap',
+        summary: 'Multi-line',
+        start: new Date('2026-06-01T00:00:00Z'),
+        description: 'Line1\nLine2',
+      },
+    ]);
+    expect(ics).toContain('DESCRIPTION:Line1\\nLine2');
+  });
+
+  it('uses CRLF line endings (RFC 5545)', () => {
+    const ics = generateICS([
+      { uid: 'u6@ap', summary: 'CRLF Check', start: new Date('2026-07-01T00:00:00Z') },
+    ]);
+    expect(ics).toContain('\r\n');
+  });
+
+  it('produces no duplicate UIDs for distinct events', () => {
+    const events = [
+      { uid: 'a@ap', summary: 'A', start: new Date('2026-01-01T00:00:00Z') },
+      { uid: 'b@ap', summary: 'B', start: new Date('2026-02-01T00:00:00Z') },
+    ];
+    const ics = generateICS(events);
+    const uids = [...ics.matchAll(/^UID:(.+)$/gm)].map((m) => m[1]);
+    expect(new Set(uids).size).toBe(uids.length);
+  });
+
+  it('returns only the envelope for an empty events array', () => {
+    const ics = generateICS([]);
+    expect(ics).not.toContain('BEGIN:VEVENT');
+  });
+});
+
+describe('downloadICS', () => {
+  beforeEach(() => {
+    // Stub browser APIs not present in jsdom
+    vi.stubGlobal('URL', {
+      createObjectURL: vi.fn(() => 'blob:mock-url'),
+      revokeObjectURL: vi.fn(),
+    });
+  });
+
+  it('creates a link element and triggers download', () => {
+    const clickSpy = vi.fn();
+    const createElementSpy = vi
+      .spyOn(document, 'createElement')
+      .mockReturnValue({ href: '', download: '', click: clickSpy } as unknown as HTMLAnchorElement);
+
+    downloadICS('export.ics', 'BEGIN:VCALENDAR\r\nEND:VCALENDAR');
+
+    expect(createElementSpy).toHaveBeenCalledWith('a');
+    expect(clickSpy).toHaveBeenCalledOnce();
+
+    createElementSpy.mockRestore();
+  });
+
+  it('sets the correct filename on the anchor element', () => {
+    const anchor = { href: '', download: '', click: vi.fn() } as unknown as HTMLAnchorElement;
+    vi.spyOn(document, 'createElement').mockReturnValue(anchor);
+
+    downloadICS('my-project.ics', 'BEGIN:VCALENDAR\r\nEND:VCALENDAR');
+
+    expect(anchor.download).toBe('my-project.ics');
+
+    vi.restoreAllMocks();
+  });
+
+  it('revokes the object URL after triggering download', () => {
+    vi.spyOn(document, 'createElement').mockReturnValue({
+      href: '',
+      download: '',
+      click: vi.fn(),
+    } as unknown as HTMLAnchorElement);
+
+    downloadICS('export.ics', 'BEGIN:VCALENDAR\r\nEND:VCALENDAR');
+
+    expect(URL.revokeObjectURL).toHaveBeenCalledWith('blob:mock-url');
+
+    vi.restoreAllMocks();
+  });
+});