Add test mode for accessibility testing (fixes crashes)

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added support for disabling touch handling on SwiftUI views via the `allowsHitTesting` modifier
 - Added SwiftUI documentation to the README.md
 - Added properties to `CalendarViewProxy` for getting the `visibleMonthRange` and `visibleDayRange` 
+- Added ability to disable `DisplayLink` animations for test purposes (to prevent crashes) with an environment variable.
 
 ### Fixed
 - Fixed an issue that could cause accessibility focus to shift unexpectedly

README.md

@@ -65,6 +65,8 @@ Features:
       - [Adding a day range indicator](#adding-a-day-range-indicator)
       - [Adding grid lines](#adding-grid-lines)
     - [Responding to day selection](#responding-to-day-selection)
+- [Testing](#testing)
+  - [Accessibility Testing](#accessibility-testing)
 - [Technical Details](#technical-details)
 - [Contributions](#contributions)
 - [Authors](#authors)
@@ -743,6 +745,46 @@ After building and running the app, tapping days should cause them to turn blue:
 
 <img width="250" alt="Day Selection Screenshot" src="Docs/Images/tutorial_day_selection.png">
 
+## Testing
+
+### Accessibility Testing
+
+If you're using accessibility testing frameworks like GTXiLib or performing automated UI testing, you may encounter issues with `CalendarView`'s DisplayLink 
+animations. To disable DisplayLink during tests, set the `HORIZON_CALENDAR_DISABLE_DISPLAY_LINK` environment variable to `true`.
+
+#### XCTest
+
+Add the environment variable to your test scheme:
+
+1. Edit your test scheme in Xcode
+2. Go to Test → Arguments → Environment Variables
+3. Add `HORIZON_CALENDAR_DISABLE_DISPLAY_LINK` = `true`
+
+Or set it programmatically in your test setup:
+```swift
+override func setUp() {
+  super.setUp()
+  setenv("HORIZON_CALENDAR_DISABLE_DISPLAY_LINK", "true", 1)
+}
+```
+
+#### Launch Arguments
+
+When launching your app for testing, pass the environment variable:
+```swift
+let app = XCUIApplication()
+app.launchEnvironment = ["HORIZON_CALENDAR_DISABLE_DISPLAY_LINK": "true"]
+app.launch()
+```
+
+#### Why This Helps
+
+CalendarView uses `CADisplayLink` for smooth scroll animations. During accessibility testing, DisplayLink callbacks can fire before the view hierarchy is fully 
+initialized, causing crashes. Disabling DisplayLink in test mode prevents these crashes while still allowing you to test the calendar's accessibility features.
+
+**Note:** When DisplayLink is disabled, scroll animations will complete immediately without animation. This is expected behavior in test mode and doesn't affect the 
+calendar's functionality or accessibility testing.
+
 ## Technical Details
 If you'd like to learn about how `HorizonCalendar` was implemented, check out the [Technical Details](Docs/TECHNICAL_DETAILS.md) document. It provides an overview of `HorizonCalendar`'s architecture, along with information about why it's not implemented using `UICollectionView`. 
 

Sources/Public/CalendarView.swift

@@ -532,6 +532,13 @@ public final class CalendarView: UIView {
     return false
   }()
 
+  /// Checks if DisplayLink animations should be disabled for testing purposes.
+  /// Set the environment variable `HORIZON_CALENDAR_DISABLE_DISPLAY_LINK=true` to disable
+  /// DisplayLink animations during accessibility testing or other UI tests.
+  private var shouldDisableDisplayLink: Bool {
+    ProcessInfo.processInfo.environment["HORIZON_CALENDAR_DISABLE_DISPLAY_LINK"] == "true"
+  }
+
   private var initialItemViewWasFocused = false {
     didSet {
       guard initialItemViewWasFocused != oldValue else { return }
@@ -833,6 +840,15 @@ public final class CalendarView: UIView {
   }
 
   private func startScrollingTowardTargetItem() {
+    // Skip DisplayLink setup if test mode is enabled
+    guard !shouldDisableDisplayLink else {
+      // Perform immediate scroll without animation when DisplayLink is disabled
+      if let scrollToItemContext {
+        finalizeScrollingTowardItem(for: scrollToItemContext)
+      }
+      return
+    }
+
     let scrollToItemDisplayLink = CADisplayLink(
       target: self,
       selector: #selector(scrollToItemDisplayLinkFired))
@@ -1041,6 +1057,9 @@ public final class CalendarView: UIView {
     func enableAutoScroll(offset: CGFloat) {
       autoScrollOffset = offset
 
+      // Skip DisplayLink setup if test mode is enabled
+      guard !shouldDisableDisplayLink else { return }
+
       if autoScrollDisplayLink == nil {
         let autoScrollDisplayLink = CADisplayLink(
           target: self,