diff --git a/src/frontend/apps/calendars/src/features/calendar/services/dav/__tests__/caldav-helpers.test.ts b/src/frontend/apps/calendars/src/features/calendar/services/dav/__tests__/caldav-helpers.test.ts
new file mode 100644
index 0000000..6237062
--- /dev/null
+++ b/src/frontend/apps/calendars/src/features/calendar/services/dav/__tests__/caldav-helpers.test.ts
@@ -0,0 +1,363 @@
+/**
+ * Tests for CalDAV Helper functions
+ */
+import {
+  escapeXml,
+  XML_NS,
+  xmlProp,
+  xmlPropOptional,
+  buildCalendarPropsXml,
+  buildMkCalendarXml,
+  buildProppatchXml,
+  sharePrivilegeToXml,
+  parseSharePrivilege,
+  buildShareeSetXml,
+  buildShareRequestXml,
+  buildUnshareRequestXml,
+  buildInviteReplyXml,
+  buildSyncCollectionXml,
+  buildPrincipalSearchXml,
+  parseCalendarComponents,
+  parseShareStatus,
+  getCalendarUrlFromEventUrl,
+} from '../caldav-helpers'
+import type { SharePrivilege } from '../types/caldav-service'
+
+describe('caldav-helpers', () => {
+  // ============================================================================
+  // XML Helpers
+  // ============================================================================
+  describe('XML Helpers', () => {
+    describe('escapeXml', () => {
+      it('escapes ampersand', () => {
+        expect(escapeXml('Tom & Jerry')).toBe('Tom & Jerry')
+      })
+
+      it('escapes less than', () => {
+        expect(escapeXml('1 < 2')).toBe('1 &lt; 2')
+      })
+
+      it('escapes greater than', () => {
+        expect(escapeXml('2 > 1')).toBe('2 &gt; 1')
+      })
+
+      it('escapes double quotes', () => {
+        expect(escapeXml('He said "hello"')).toBe('He said &quot;hello&quot;')
+      })
+
+      it('escapes single quotes', () => {
+        expect(escapeXml("It's fine")).toBe('It&apos;s fine')
+      })
+
+      it('escapes multiple characters', () => {
+        expect(escapeXml('<tag attr="val">text & more</tag>')).toBe(
+          '&lt;tag attr=&quot;val&quot;&gt;text &amp; more&lt;/tag&gt;'
+        )
+      })
+    })
+
+    describe('XML_NS', () => {
+      it('contains correct namespaces', () => {
+        expect(XML_NS.DAV).toBe('xmlns:D="DAV:"')
+        expect(XML_NS.CALDAV).toBe('xmlns:C="urn:ietf:params:xml:ns:caldav"')
+        expect(XML_NS.APPLE).toBe('xmlns:A="http://apple.com/ns/ical/"')
+        expect(XML_NS.CS).toBe('xmlns:CS="http://calendarserver.org/ns/"')
+      })
+    })
+
+    describe('xmlProp', () => {
+      it('creates XML element with namespace', () => {
+        expect(xmlProp('D', 'displayname', 'My Calendar')).toBe(
+          '<D:displayname>My Calendar</D:displayname>'
+        )
+      })
+
+      it('escapes value content', () => {
+        expect(xmlProp('D', 'displayname', 'Tom & Jerry')).toBe(
+          '<D:displayname>Tom &amp; Jerry</D:displayname>'
+        )
+      })
+    })
+
+    describe('xmlPropOptional', () => {
+      it('returns element when value is defined', () => {
+        expect(xmlPropOptional('D', 'displayname', 'Test')).toBe(
+          '<D:displayname>Test</D:displayname>'
+        )
+      })
+
+      it('returns empty string when value is undefined', () => {
+        expect(xmlPropOptional('D', 'displayname', undefined)).toBe('')
+      })
+    })
+  })
+
+  // ============================================================================
+  // Calendar Property Builders
+  // ============================================================================
+  describe('Calendar Property Builders', () => {
+    describe('buildCalendarPropsXml', () => {
+      it('builds displayName property', () => {
+        const result = buildCalendarPropsXml({ displayName: 'My Calendar' })
+        expect(result).toContain('<D:displayname>My Calendar</D:displayname>')
+      })
+
+      it('builds description property', () => {
+        const result = buildCalendarPropsXml({ description: 'A test calendar' })
+        expect(result).toContain('<C:calendar-description>A test calendar</C:calendar-description>')
+      })
+
+      it('builds color property', () => {
+        const result = buildCalendarPropsXml({ color: '#ff0000' })
+        expect(result).toContain('<A:calendar-color>#ff0000</A:calendar-color>')
+      })
+
+      it('builds components property', () => {
+        const result = buildCalendarPropsXml({ components: ['VEVENT', 'VTODO'] })
+        expect(result.join('')).toContain('supported-calendar-component-set')
+        expect(result.join('')).toContain('<C:comp name="VEVENT"/>')
+        expect(result.join('')).toContain('<C:comp name="VTODO"/>')
+      })
+
+      it('builds multiple properties', () => {
+        const result = buildCalendarPropsXml({
+          displayName: 'Work',
+          description: 'Work calendar',
+          color: '#0000ff',
+        })
+        expect(result).toHaveLength(3)
+      })
+    })
+
+    describe('buildMkCalendarXml', () => {
+      it('creates valid MKCALENDAR XML', () => {
+        const result = buildMkCalendarXml({ displayName: 'New Calendar' })
+        expect(result).toContain('<?xml version="1.0"')
+        expect(result).toContain('<C:mkcalendar')
+        expect(result).toContain('xmlns:D="DAV:"')
+        expect(result).toContain('xmlns:C="urn:ietf:params:xml:ns:caldav"')
+        expect(result).toContain('<D:displayname>New Calendar</D:displayname>')
+        expect(result).toContain('</C:mkcalendar>')
+      })
+    })
+
+    describe('buildProppatchXml', () => {
+      it('creates valid PROPPATCH XML', () => {
+        const result = buildProppatchXml({ displayName: 'Updated Name' })
+        expect(result).toContain('<?xml version="1.0"')
+        expect(result).toContain('<D:propertyupdate')
+        expect(result).toContain('<D:set>')
+        expect(result).toContain('<D:displayname>Updated Name</D:displayname>')
+      })
+    })
+  })
+
+  // ============================================================================
+  // Sharing XML Builders
+  // ============================================================================
+  describe('Sharing XML Builders', () => {
+    describe('sharePrivilegeToXml', () => {
+      it('converts read privilege', () => {
+        expect(sharePrivilegeToXml('read')).toBe('<CS:read/>')
+      })
+
+      it('converts read-write privilege', () => {
+        expect(sharePrivilegeToXml('read-write')).toBe('<CS:read-write/>')
+      })
+
+      it('converts admin privilege', () => {
+        expect(sharePrivilegeToXml('admin')).toBe('<CS:admin/>')
+      })
+
+      it('defaults to read for unknown', () => {
+        expect(sharePrivilegeToXml('unknown' as SharePrivilege)).toBe('<CS:read/>')
+      })
+    })
+
+    describe('parseSharePrivilege', () => {
+      it('returns read-write when present', () => {
+        expect(parseSharePrivilege({ 'read-write': true })).toBe('read-write')
+      })
+
+      it('returns admin when present', () => {
+        expect(parseSharePrivilege({ admin: true })).toBe('admin')
+      })
+
+      it('returns read as default', () => {
+        expect(parseSharePrivilege({})).toBe('read')
+        expect(parseSharePrivilege(null)).toBe('read')
+      })
+    })
+
+    describe('buildShareeSetXml', () => {
+      it('builds basic sharee XML', () => {
+        const result = buildShareeSetXml({
+          href: 'mailto:user@example.com',
+          privilege: 'read-write',
+        })
+        expect(result).toContain('<CS:set>')
+        expect(result).toContain('<D:href>mailto:user@example.com</D:href>')
+        expect(result).toContain('<CS:read-write/>')
+      })
+
+      it('includes displayName when provided', () => {
+        const result = buildShareeSetXml({
+          href: 'mailto:user@example.com',
+          displayName: 'John Doe',
+          privilege: 'read',
+        })
+        expect(result).toContain('<CS:common-name>John Doe</CS:common-name>')
+      })
+
+      it('includes summary when provided', () => {
+        const result = buildShareeSetXml({
+          href: 'mailto:user@example.com',
+          summary: 'Shared calendar',
+          privilege: 'read',
+        })
+        expect(result).toContain('<CS:summary>Shared calendar</CS:summary>')
+      })
+    })
+
+    describe('buildShareRequestXml', () => {
+      it('builds share request with multiple sharees', () => {
+        const result = buildShareRequestXml([
+          { href: 'mailto:user1@example.com', privilege: 'read' },
+          { href: 'mailto:user2@example.com', privilege: 'read-write' },
+        ])
+        expect(result).toContain('<?xml version="1.0"')
+        expect(result).toContain('<CS:share')
+        expect(result).toContain('mailto:user1@example.com')
+        expect(result).toContain('mailto:user2@example.com')
+      })
+    })
+
+    describe('buildUnshareRequestXml', () => {
+      it('builds unshare request', () => {
+        const result = buildUnshareRequestXml('mailto:user@example.com')
+        expect(result).toContain('<CS:share')
+        expect(result).toContain('<CS:remove>')
+        expect(result).toContain('<D:href>mailto:user@example.com</D:href>')
+      })
+    })
+
+    describe('buildInviteReplyXml', () => {
+      it('builds accept reply', () => {
+        const result = buildInviteReplyXml('invite-123', true)
+        expect(result).toContain('<CS:invite-reply')
+        expect(result).toContain('<CS:in-reply-to>invite-123</CS:in-reply-to>')
+        expect(result).toContain('<CS:invite-accepted/>')
+      })
+
+      it('builds decline reply', () => {
+        const result = buildInviteReplyXml('invite-123', false)
+        expect(result).toContain('<CS:invite-declined/>')
+      })
+    })
+  })
+
+  // ============================================================================
+  // Sync XML Builders
+  // ============================================================================
+  describe('Sync XML Builders', () => {
+    describe('buildSyncCollectionXml', () => {
+      it('builds sync-collection XML', () => {
+        const result = buildSyncCollectionXml({
+          syncToken: 'token-123',
+        })
+        expect(result).toContain('<?xml version="1.0"')
+        expect(result).toContain('<D:sync-collection')
+        expect(result).toContain('<D:sync-token>token-123</D:sync-token>')
+        expect(result).toContain('<D:sync-level>1</D:sync-level>')
+        expect(result).toContain('<D:getetag/>')
+        expect(result).toContain('<C:calendar-data/>')
+      })
+
+      it('uses custom sync level', () => {
+        const result = buildSyncCollectionXml({
+          syncToken: 'token-123',
+          syncLevel: 'infinite',
+        })
+        expect(result).toContain('<D:sync-level>infinite</D:sync-level>')
+      })
+    })
+  })
+
+  // ============================================================================
+  // Principal Search XML Builder
+  // ============================================================================
+  describe('Principal Search XML Builder', () => {
+    describe('buildPrincipalSearchXml', () => {
+      it('builds principal search XML', () => {
+        const result = buildPrincipalSearchXml('john')
+        expect(result).toContain('<?xml version="1.0"')
+        expect(result).toContain('<D:principal-property-search')
+        expect(result).toContain('<D:match>john</D:match>')
+        expect(result).toContain('<D:displayname/>')
+        expect(result).toContain('<C:calendar-home-set')
+      })
+
+      it('escapes query', () => {
+        const result = buildPrincipalSearchXml('Tom & Jerry')
+        expect(result).toContain('<D:match>Tom &amp; Jerry</D:match>')
+      })
+    })
+  })
+
+  // ============================================================================
+  // Response Parsing Helpers
+  // ============================================================================
+  describe('Response Parsing Helpers', () => {
+    describe('parseCalendarComponents', () => {
+      it('returns undefined for empty input', () => {
+        expect(parseCalendarComponents(null)).toBeUndefined()
+        expect(parseCalendarComponents(undefined)).toBeUndefined()
+      })
+
+      it('parses array of components', () => {
+        const input = {
+          comp: [
+            { _attributes: { name: 'VEVENT' } },
+            { _attributes: { name: 'VTODO' } },
+          ],
+        }
+        const result = parseCalendarComponents(input)
+        expect(result).toEqual(['VEVENT', 'VTODO'])
+      })
+
+      it('parses single component', () => {
+        const input = {
+          comp: { _attributes: { name: 'VEVENT' } },
+        }
+        const result = parseCalendarComponents(input)
+        expect(result).toEqual(['VEVENT'])
+      })
+    })
+
+    describe('parseShareStatus', () => {
+      it('returns accepted when accepted is truthy', () => {
+        expect(parseShareStatus(true, false)).toBe('accepted')
+      })
+
+      it('returns pending when noResponse is truthy', () => {
+        expect(parseShareStatus(false, true)).toBe('pending')
+      })
+
+      it('returns declined as default', () => {
+        expect(parseShareStatus(false, false)).toBe('declined')
+      })
+    })
+
+    describe('getCalendarUrlFromEventUrl', () => {
+      it('extracts calendar URL from event URL', () => {
+        const eventUrl = '/calendars/user/calendar-1/event-123.ics'
+        expect(getCalendarUrlFromEventUrl(eventUrl)).toBe('/calendars/user/calendar-1/')
+      })
+
+      it('handles URL without trailing slash', () => {
+        const eventUrl = '/calendars/user/calendar-1/event.ics'
+        expect(getCalendarUrlFromEventUrl(eventUrl)).toBe('/calendars/user/calendar-1/')
+      })
+    })
+  })
+})
diff --git a/src/frontend/apps/calendars/src/features/calendar/services/dav/__tests__/event-calendar-helper.test.ts b/src/frontend/apps/calendars/src/features/calendar/services/dav/__tests__/event-calendar-helper.test.ts
new file mode 100644
index 0000000..010f284
--- /dev/null
+++ b/src/frontend/apps/calendars/src/features/calendar/services/dav/__tests__/event-calendar-helper.test.ts
@@ -0,0 +1,710 @@
+/**
+ * Tests for Event Calendar Helper functions
+ */
+import {
+  formatEventCalendarDate,
+  parseEventCalendarDate,
+  isSameDay,
+  startOfDay,
+  endOfDay,
+  startOfWeek,
+  endOfWeek,
+  startOfMonth,
+  endOfMonth,
+  parseDuration,
+  durationToSeconds,
+  secondsToDuration,
+  formatDuration,
+  addDuration,
+  subtractDuration,
+  isAllDayEvent,
+  isMultiDayEvent,
+  getEventDurationMinutes,
+  eventOverlapsRange,
+  filterEventsInRange,
+  sortEventsByStart,
+  groupEventsByDate,
+  moveEvent,
+  resizeEvent,
+  getViewDateRange,
+  isListView,
+  isResourceView,
+  isTimelineView,
+  findResourceById,
+  flattenResources,
+  getEventsForResource,
+  icsDateToJsDate,
+  jsDateToIcsDate,
+  isIcsEventAllDay,
+  getIcsEventTimezone,
+  hasRecurrence,
+  isRecurringInstance,
+  describeRecurrence,
+  stringToColor,
+  isColorDark,
+  getContrastingTextColor,
+  getAttendeeDisplayName,
+  getAttendeeStatusIcon,
+  getAttendeeStatusColor,
+} from '../helpers/event-calendar-helper'
+import type { EventCalendarEvent, EventCalendarResource, EventCalendarDuration } from '../types/event-calendar'
+import type { IcsDateObject, IcsEvent, IcsRecurrenceRule } from 'ts-ics'
+
+describe('event-calendar-helper', () => {
+  // ============================================================================
+  // Date/Time Helpers
+  // ============================================================================
+  describe('Date/Time Helpers', () => {
+    describe('formatEventCalendarDate', () => {
+      it('returns ISO string for Date object', () => {
+        const date = new Date('2025-01-15T10:30:00.000Z')
+        const result = formatEventCalendarDate(date)
+        expect(result).toBe('2025-01-15T10:30:00.000Z')
+      })
+
+      it('returns string as-is', () => {
+        const dateStr = '2025-01-15T10:30:00.000Z'
+        expect(formatEventCalendarDate(dateStr)).toBe(dateStr)
+      })
+    })
+
+    describe('parseEventCalendarDate', () => {
+      it('returns Date object for string input', () => {
+        const result = parseEventCalendarDate('2025-01-15T10:30:00.000Z')
+        expect(result instanceof Date).toBe(true)
+        expect(result.toISOString()).toBe('2025-01-15T10:30:00.000Z')
+      })
+
+      it('returns same Date object for Date input', () => {
+        const date = new Date('2025-01-15T10:30:00.000Z')
+        expect(parseEventCalendarDate(date)).toBe(date)
+      })
+    })
+
+    describe('isSameDay', () => {
+      it('returns true for same day', () => {
+        const date1 = new Date('2025-01-15T08:00:00.000Z')
+        const date2 = new Date('2025-01-15T20:00:00.000Z')
+        expect(isSameDay(date1, date2)).toBe(true)
+      })
+
+      it('returns false for different days', () => {
+        // Using dates that are clearly different days in any timezone
+        const date1 = new Date('2025-01-15T12:00:00.000Z')
+        const date2 = new Date('2025-01-17T12:00:00.000Z')
+        expect(isSameDay(date1, date2)).toBe(false)
+      })
+    })
+
+    describe('startOfDay', () => {
+      it('returns start of day', () => {
+        const date = new Date('2025-01-15T14:30:45.123Z')
+        const result = startOfDay(date)
+        expect(result.getHours()).toBe(0)
+        expect(result.getMinutes()).toBe(0)
+        expect(result.getSeconds()).toBe(0)
+        expect(result.getMilliseconds()).toBe(0)
+      })
+    })
+
+    describe('endOfDay', () => {
+      it('returns end of day', () => {
+        const date = new Date('2025-01-15T14:30:45.123Z')
+        const result = endOfDay(date)
+        expect(result.getHours()).toBe(23)
+        expect(result.getMinutes()).toBe(59)
+        expect(result.getSeconds()).toBe(59)
+        expect(result.getMilliseconds()).toBe(999)
+      })
+    })
+
+    describe('startOfWeek', () => {
+      it('returns Monday for firstDay=1 (default)', () => {
+        const date = new Date(2025, 0, 15) // Wednesday
+        const result = startOfWeek(date)
+        expect(result.getDay()).toBe(1) // Monday
+      })
+
+      it('returns Sunday for firstDay=0', () => {
+        const date = new Date(2025, 0, 15) // Wednesday
+        const result = startOfWeek(date, 0)
+        expect(result.getDay()).toBe(0) // Sunday
+      })
+    })
+
+    describe('endOfWeek', () => {
+      it('returns Sunday for firstDay=1 (Monday start)', () => {
+        const date = new Date(2025, 0, 15) // Wednesday
+        const result = endOfWeek(date)
+        expect(result.getDay()).toBe(0) // Sunday
+      })
+    })
+
+    describe('startOfMonth', () => {
+      it('returns first day of month', () => {
+        const date = new Date(2025, 0, 15)
+        const result = startOfMonth(date)
+        expect(result.getDate()).toBe(1)
+        expect(result.getMonth()).toBe(0)
+      })
+    })
+
+    describe('endOfMonth', () => {
+      it('returns last day of month', () => {
+        const date = new Date(2025, 0, 15) // January
+        const result = endOfMonth(date)
+        expect(result.getDate()).toBe(31)
+        expect(result.getMonth()).toBe(0)
+      })
+
+      it('handles February in leap year', () => {
+        const date = new Date(2024, 1, 15) // February 2024 (leap year)
+        const result = endOfMonth(date)
+        expect(result.getDate()).toBe(29)
+      })
+    })
+  })
+
+  // ============================================================================
+  // Duration Helpers
+  // ============================================================================
+  describe('Duration Helpers', () => {
+    describe('parseDuration', () => {
+      it('parses number as total seconds', () => {
+        const result = parseDuration(3665)
+        expect(result.hours).toBe(1)
+        expect(result.minutes).toBe(1)
+        expect(result.seconds).toBe(5)
+      })
+
+      it('parses hh:mm string', () => {
+        const result = parseDuration('02:30')
+        expect(result.hours).toBe(2)
+        expect(result.minutes).toBe(30)
+      })
+
+      it('parses hh:mm:ss string', () => {
+        const result = parseDuration('01:30:45')
+        expect(result.hours).toBe(1)
+        expect(result.minutes).toBe(30)
+        expect(result.seconds).toBe(45)
+      })
+
+      it('returns object as-is', () => {
+        const duration = { hours: 1, minutes: 30 }
+        expect(parseDuration(duration)).toBe(duration)
+      })
+    })
+
+    describe('durationToSeconds', () => {
+      it('converts duration to total seconds', () => {
+        const duration: EventCalendarDuration = { hours: 1, minutes: 30, seconds: 15 }
+        expect(durationToSeconds(duration)).toBe(5415)
+      })
+
+      it('handles days', () => {
+        const duration: EventCalendarDuration = { days: 1, hours: 2 }
+        expect(durationToSeconds(duration)).toBe(93600)
+      })
+    })
+
+    describe('secondsToDuration', () => {
+      it('converts seconds to duration object', () => {
+        const result = secondsToDuration(5415)
+        expect(result.hours).toBe(1)
+        expect(result.minutes).toBe(30)
+        expect(result.seconds).toBe(15)
+      })
+
+      it('includes days when appropriate', () => {
+        const result = secondsToDuration(93600)
+        expect(result.days).toBe(1)
+        expect(result.hours).toBe(2)
+      })
+    })
+
+    describe('formatDuration', () => {
+      it('formats as hh:mm', () => {
+        const duration: EventCalendarDuration = { hours: 2, minutes: 30 }
+        expect(formatDuration(duration)).toBe('02:30')
+      })
+
+      it('formats as hh:mm:ss when seconds present', () => {
+        const duration: EventCalendarDuration = { hours: 1, minutes: 5, seconds: 30 }
+        expect(formatDuration(duration)).toBe('01:05:30')
+      })
+    })
+
+    describe('addDuration', () => {
+      it('adds duration to date', () => {
+        const date = new Date('2025-01-15T10:00:00.000Z')
+        const duration: EventCalendarDuration = { hours: 2, minutes: 30 }
+        const result = addDuration(date, duration)
+        expect(result.toISOString()).toBe('2025-01-15T12:30:00.000Z')
+      })
+    })
+
+    describe('subtractDuration', () => {
+      it('subtracts duration from date', () => {
+        const date = new Date('2025-01-15T12:30:00.000Z')
+        const duration: EventCalendarDuration = { hours: 2, minutes: 30 }
+        const result = subtractDuration(date, duration)
+        expect(result.toISOString()).toBe('2025-01-15T10:00:00.000Z')
+      })
+    })
+  })
+
+  // ============================================================================
+  // Event Helpers
+  // ============================================================================
+  describe('Event Helpers', () => {
+    describe('isAllDayEvent', () => {
+      it('returns true when allDay is true', () => {
+        const event = { id: '1', start: new Date(), allDay: true } as EventCalendarEvent
+        expect(isAllDayEvent(event)).toBe(true)
+      })
+
+      it('returns false when allDay is false', () => {
+        const event = { id: '1', start: new Date(), allDay: false } as EventCalendarEvent
+        expect(isAllDayEvent(event)).toBe(false)
+      })
+    })
+
+    describe('isMultiDayEvent', () => {
+      it('returns false for same day event', () => {
+        const event = {
+          id: '1',
+          start: new Date('2025-01-15T10:00:00.000Z'),
+          end: new Date('2025-01-15T12:00:00.000Z'),
+        } as EventCalendarEvent
+        expect(isMultiDayEvent(event)).toBe(false)
+      })
+
+      it('returns true for multi-day event', () => {
+        const event = {
+          id: '1',
+          start: new Date('2025-01-15T10:00:00.000Z'),
+          end: new Date('2025-01-16T12:00:00.000Z'),
+        } as EventCalendarEvent
+        expect(isMultiDayEvent(event)).toBe(true)
+      })
+    })
+
+    describe('getEventDurationMinutes', () => {
+      it('calculates duration in minutes', () => {
+        const event = {
+          id: '1',
+          start: new Date('2025-01-15T10:00:00.000Z'),
+          end: new Date('2025-01-15T11:30:00.000Z'),
+        } as EventCalendarEvent
+        expect(getEventDurationMinutes(event)).toBe(90)
+      })
+    })
+
+    describe('eventOverlapsRange', () => {
+      it('returns true when event overlaps range', () => {
+        const event = {
+          id: '1',
+          start: new Date('2025-01-15T10:00:00.000Z'),
+          end: new Date('2025-01-15T12:00:00.000Z'),
+        } as EventCalendarEvent
+        const result = eventOverlapsRange(
+          event,
+          '2025-01-15T11:00:00.000Z',
+          '2025-01-15T14:00:00.000Z'
+        )
+        expect(result).toBe(true)
+      })
+
+      it('returns false when event is before range', () => {
+        const event = {
+          id: '1',
+          start: new Date('2025-01-15T08:00:00.000Z'),
+          end: new Date('2025-01-15T09:00:00.000Z'),
+        } as EventCalendarEvent
+        const result = eventOverlapsRange(
+          event,
+          '2025-01-15T10:00:00.000Z',
+          '2025-01-15T12:00:00.000Z'
+        )
+        expect(result).toBe(false)
+      })
+    })
+
+    describe('filterEventsInRange', () => {
+      it('filters events within range', () => {
+        const events = [
+          { id: '1', start: new Date('2025-01-15T10:00:00.000Z'), end: new Date('2025-01-15T11:00:00.000Z') },
+          { id: '2', start: new Date('2025-01-14T10:00:00.000Z'), end: new Date('2025-01-14T11:00:00.000Z') },
+          { id: '3', start: new Date('2025-01-15T14:00:00.000Z'), end: new Date('2025-01-15T15:00:00.000Z') },
+        ] as EventCalendarEvent[]
+
+        const result = filterEventsInRange(
+          events,
+          '2025-01-15T09:00:00.000Z',
+          '2025-01-15T12:00:00.000Z'
+        )
+        expect(result).toHaveLength(1)
+        expect(result[0].id).toBe('1')
+      })
+    })
+
+    describe('sortEventsByStart', () => {
+      it('sorts events by start date', () => {
+        const events = [
+          { id: '2', start: new Date('2025-01-15T14:00:00.000Z') },
+          { id: '1', start: new Date('2025-01-15T10:00:00.000Z') },
+          { id: '3', start: new Date('2025-01-15T12:00:00.000Z') },
+        ] as EventCalendarEvent[]
+
+        const result = sortEventsByStart(events)
+        expect(result.map(e => e.id)).toEqual(['1', '3', '2'])
+      })
+    })
+
+    describe('groupEventsByDate', () => {
+      it('groups events by date', () => {
+        const events = [
+          { id: '1', start: new Date('2025-01-15T10:00:00.000Z') },
+          { id: '2', start: new Date('2025-01-15T14:00:00.000Z') },
+          { id: '3', start: new Date('2025-01-16T10:00:00.000Z') },
+        ] as EventCalendarEvent[]
+
+        const result = groupEventsByDate(events)
+        expect(result.size).toBe(2)
+      })
+    })
+
+    describe('moveEvent', () => {
+      it('moves event preserving duration', () => {
+        const event = {
+          id: '1',
+          start: new Date('2025-01-15T10:00:00.000Z'),
+          end: new Date('2025-01-15T12:00:00.000Z'),
+        } as EventCalendarEvent
+
+        const result = moveEvent(event, '2025-01-16T14:00:00.000Z')
+        expect((result.start as Date).toISOString()).toBe('2025-01-16T14:00:00.000Z')
+        expect((result.end as Date).toISOString()).toBe('2025-01-16T16:00:00.000Z')
+      })
+    })
+
+    describe('resizeEvent', () => {
+      it('changes event end time', () => {
+        const event = {
+          id: '1',
+          start: new Date('2025-01-15T10:00:00.000Z'),
+          end: new Date('2025-01-15T12:00:00.000Z'),
+        } as EventCalendarEvent
+
+        const result = resizeEvent(event, '2025-01-15T14:00:00.000Z')
+        expect((result.end as Date).toISOString()).toBe('2025-01-15T14:00:00.000Z')
+      })
+    })
+  })
+
+  // ============================================================================
+  // View Helpers
+  // ============================================================================
+  describe('View Helpers', () => {
+    describe('getViewDateRange', () => {
+      it('returns day range for dayGridDay view', () => {
+        const { start, end } = getViewDateRange('dayGridDay', '2025-01-15')
+        expect(start.getDate()).toBe(15)
+        expect(end.getDate()).toBe(15)
+      })
+
+      it('returns month range for dayGridMonth view', () => {
+        const { start, end } = getViewDateRange('dayGridMonth', '2025-01-15')
+        expect(start.getDate()).toBe(1)
+        expect(end.getDate()).toBe(31)
+      })
+    })
+
+    describe('isListView', () => {
+      it('returns true for list views', () => {
+        expect(isListView('listDay')).toBe(true)
+        expect(isListView('listWeek')).toBe(true)
+      })
+
+      it('returns false for non-list views', () => {
+        expect(isListView('dayGridMonth')).toBe(false)
+      })
+    })
+
+    describe('isResourceView', () => {
+      it('returns true for resource views', () => {
+        expect(isResourceView('resourceTimeGridDay')).toBe(true)
+      })
+
+      it('returns false for non-resource views', () => {
+        expect(isResourceView('dayGridMonth')).toBe(false)
+      })
+    })
+
+    describe('isTimelineView', () => {
+      it('returns true for timeline views', () => {
+        expect(isTimelineView('resourceTimelineDay')).toBe(true)
+      })
+
+      it('returns false for non-timeline views', () => {
+        expect(isTimelineView('dayGridMonth')).toBe(false)
+      })
+    })
+  })
+
+  // ============================================================================
+  // Resource Helpers
+  // ============================================================================
+  describe('Resource Helpers', () => {
+    describe('findResourceById', () => {
+      it('finds resource at top level', () => {
+        const resources: EventCalendarResource[] = [
+          { id: '1', title: 'Room A' },
+          { id: '2', title: 'Room B' },
+        ]
+        const result = findResourceById(resources, '2')
+        expect(result?.title).toBe('Room B')
+      })
+
+      it('finds nested resource', () => {
+        const resources: EventCalendarResource[] = [
+          { id: '1', title: 'Building A', children: [
+            { id: '1-1', title: 'Room 101' },
+          ]},
+        ]
+        const result = findResourceById(resources, '1-1')
+        expect(result?.title).toBe('Room 101')
+      })
+    })
+
+    describe('flattenResources', () => {
+      it('flattens nested resources', () => {
+        const resources: EventCalendarResource[] = [
+          { id: '1', title: 'Building A', children: [
+            { id: '1-1', title: 'Room 101' },
+            { id: '1-2', title: 'Room 102' },
+          ]},
+          { id: '2', title: 'Building B' },
+        ]
+        const result = flattenResources(resources)
+        expect(result).toHaveLength(4)
+      })
+    })
+
+    describe('getEventsForResource', () => {
+      it('filters events by resource', () => {
+        const events = [
+          { id: '1', start: new Date(), resourceIds: ['room-1'] },
+          { id: '2', start: new Date(), resourceIds: ['room-2'] },
+          { id: '3', start: new Date(), resourceIds: ['room-1', 'room-2'] },
+        ] as EventCalendarEvent[]
+
+        const result = getEventsForResource(events, 'room-1')
+        expect(result).toHaveLength(2)
+        expect(result.map(e => e.id)).toEqual(['1', '3'])
+      })
+    })
+  })
+
+  // ============================================================================
+  // ICS Conversion Helpers
+  // ============================================================================
+  describe('ICS Conversion Helpers', () => {
+    describe('icsDateToJsDate', () => {
+      it('returns local date when present', () => {
+        const localDate = new Date('2025-01-15T11:00:00.000Z')
+        const icsDate: IcsDateObject = {
+          type: 'DATE-TIME',
+          date: new Date('2025-01-15T10:00:00.000Z'),
+          local: { date: localDate, timezone: 'Europe/Paris', tzoffset: '+0100' },
+        }
+        expect(icsDateToJsDate(icsDate)).toBe(localDate)
+      })
+
+      it('returns UTC date when no local', () => {
+        const utcDate = new Date('2025-01-15T10:00:00.000Z')
+        const icsDate: IcsDateObject = {
+          type: 'DATE-TIME',
+          date: utcDate,
+        }
+        expect(icsDateToJsDate(icsDate)).toBe(utcDate)
+      })
+    })
+
+    describe('jsDateToIcsDate', () => {
+      it('creates DATE type for all-day', () => {
+        const date = new Date('2025-01-15T00:00:00.000Z')
+        const result = jsDateToIcsDate(date, true)
+        expect(result.type).toBe('DATE')
+      })
+
+      it('creates DATE-TIME type with timezone', () => {
+        const date = new Date('2025-01-15T10:00:00.000Z')
+        const result = jsDateToIcsDate(date, false, 'Europe/Paris')
+        expect(result.type).toBe('DATE-TIME')
+        expect(result.local?.timezone).toBe('Europe/Paris')
+      })
+    })
+
+    describe('isIcsEventAllDay', () => {
+      it('returns true for DATE type start', () => {
+        const event = {
+          uid: 'test',
+          stamp: { date: new Date() },
+          start: { type: 'DATE', date: new Date() },
+        } as IcsEvent
+        expect(isIcsEventAllDay(event)).toBe(true)
+      })
+    })
+
+    describe('getIcsEventTimezone', () => {
+      it('returns timezone from start local', () => {
+        const event = {
+          uid: 'test',
+          stamp: { date: new Date() },
+          start: {
+            type: 'DATE-TIME',
+            date: new Date(),
+            local: { date: new Date(), timezone: 'Europe/Paris', tzoffset: '+0100' },
+          },
+        } as IcsEvent
+        expect(getIcsEventTimezone(event)).toBe('Europe/Paris')
+      })
+    })
+  })
+
+  // ============================================================================
+  // Recurrence Helpers
+  // ============================================================================
+  describe('Recurrence Helpers', () => {
+    describe('hasRecurrence', () => {
+      it('returns true when recurrenceRule exists', () => {
+        const event = {
+          uid: 'test',
+          stamp: { date: new Date() },
+          start: { type: 'DATE-TIME', date: new Date() },
+          recurrenceRule: { frequency: 'DAILY' },
+        } as IcsEvent
+        expect(hasRecurrence(event)).toBe(true)
+      })
+    })
+
+    describe('isRecurringInstance', () => {
+      it('returns true when recurrenceId exists', () => {
+        const event = {
+          uid: 'test',
+          stamp: { date: new Date() },
+          start: { type: 'DATE-TIME', date: new Date() },
+          recurrenceId: { value: { type: 'DATE-TIME', date: new Date() } },
+        } as IcsEvent
+        expect(isRecurringInstance(event)).toBe(true)
+      })
+    })
+
+    describe('describeRecurrence', () => {
+      it('describes daily recurrence', () => {
+        const rule: IcsRecurrenceRule = { frequency: 'DAILY' }
+        expect(describeRecurrence(rule)).toBe('Every day')
+      })
+
+      it('describes weekly with interval', () => {
+        const rule: IcsRecurrenceRule = { frequency: 'WEEKLY', interval: 2 }
+        expect(describeRecurrence(rule)).toBe('Every 2 weeks')
+      })
+
+      it('describes with count', () => {
+        const rule: IcsRecurrenceRule = { frequency: 'DAILY', count: 5 }
+        expect(describeRecurrence(rule)).toContain('5 times')
+      })
+    })
+  })
+
+  // ============================================================================
+  // Color Helpers
+  // ============================================================================
+  describe('Color Helpers', () => {
+    describe('stringToColor', () => {
+      it('generates consistent color for same string', () => {
+        const color1 = stringToColor('Calendar A')
+        const color2 = stringToColor('Calendar A')
+        expect(color1).toBe(color2)
+      })
+
+      it('generates different colors for different strings', () => {
+        const color1 = stringToColor('Calendar A')
+        const color2 = stringToColor('Calendar B')
+        expect(color1).not.toBe(color2)
+      })
+
+      it('returns valid HSL color', () => {
+        const color = stringToColor('Test')
+        expect(color).toMatch(/^hsl\(\d+, 65%, 50%\)$/)
+      })
+    })
+
+    describe('isColorDark', () => {
+      it('returns true for dark hex colors', () => {
+        expect(isColorDark('#000000')).toBe(true)
+        expect(isColorDark('#333333')).toBe(true)
+      })
+
+      it('returns false for light hex colors', () => {
+        expect(isColorDark('#ffffff')).toBe(false)
+        expect(isColorDark('#eeeeee')).toBe(false)
+      })
+
+      it('handles short hex format', () => {
+        expect(isColorDark('#000')).toBe(true)
+        expect(isColorDark('#fff')).toBe(false)
+      })
+
+      it('handles rgb format', () => {
+        expect(isColorDark('rgb(0, 0, 0)')).toBe(true)
+        expect(isColorDark('rgb(255, 255, 255)')).toBe(false)
+      })
+    })
+
+    describe('getContrastingTextColor', () => {
+      it('returns white for dark backgrounds', () => {
+        expect(getContrastingTextColor('#000000')).toBe('#ffffff')
+      })
+
+      it('returns black for light backgrounds', () => {
+        expect(getContrastingTextColor('#ffffff')).toBe('#000000')
+      })
+    })
+  })
+
+  // ============================================================================
+  // Attendee Helpers
+  // ============================================================================
+  describe('Attendee Helpers', () => {
+    describe('getAttendeeDisplayName', () => {
+      it('returns name when present', () => {
+        expect(getAttendeeDisplayName({ name: 'John Doe', email: 'john@example.com' })).toBe('John Doe')
+      })
+
+      it('returns email when no name', () => {
+        expect(getAttendeeDisplayName({ email: 'john@example.com' })).toBe('john@example.com')
+      })
+    })
+
+    describe('getAttendeeStatusIcon', () => {
+      it('returns correct icons', () => {
+        expect(getAttendeeStatusIcon('ACCEPTED')).toBe('✓')
+        expect(getAttendeeStatusIcon('DECLINED')).toBe('✗')
+        expect(getAttendeeStatusIcon('TENTATIVE')).toBe('?')
+        expect(getAttendeeStatusIcon('NEEDS-ACTION')).toBe('○')
+      })
+    })
+
+    describe('getAttendeeStatusColor', () => {
+      it('returns correct colors', () => {
+        expect(getAttendeeStatusColor('ACCEPTED')).toBe('#22c55e')
+        expect(getAttendeeStatusColor('DECLINED')).toBe('#ef4444')
+        expect(getAttendeeStatusColor('TENTATIVE')).toBe('#f59e0b')
+      })
+    })
+  })
+})
diff --git a/src/frontend/apps/calendars/src/features/calendar/services/dav/__tests__/ics-helper.test.ts b/src/frontend/apps/calendars/src/features/calendar/services/dav/__tests__/ics-helper.test.ts
new file mode 100644
index 0000000..5787ef4
--- /dev/null
+++ b/src/frontend/apps/calendars/src/features/calendar/services/dav/__tests__/ics-helper.test.ts
@@ -0,0 +1,41 @@
+/**
+ * Tests for ICS Helper functions
+ */
+import type { IcsEvent } from 'ts-ics'
+import { isEventAllDay } from '../helpers/ics-helper'
+
+describe('ics-helper', () => {
+  describe('isEventAllDay', () => {
+    it('returns true when start type is DATE', () => {
+      const event = {
+        start: { type: 'DATE', date: new Date() },
+        uid: 'test',
+        stamp: { date: new Date() },
+      } as IcsEvent
+
+      expect(isEventAllDay(event)).toBe(true)
+    })
+
+    it('returns true when end type is DATE', () => {
+      const event = {
+        start: { type: 'DATE-TIME', date: new Date() },
+        end: { type: 'DATE', date: new Date() },
+        uid: 'test',
+        stamp: { date: new Date() },
+      } as IcsEvent
+
+      expect(isEventAllDay(event)).toBe(true)
+    })
+
+    it('returns false when both start and end are DATE-TIME', () => {
+      const event = {
+        start: { type: 'DATE-TIME', date: new Date() },
+        end: { type: 'DATE-TIME', date: new Date() },
+        uid: 'test',
+        stamp: { date: new Date() },
+      } as IcsEvent
+
+      expect(isEventAllDay(event)).toBe(false)
+    })
+  })
+})