diff --git a/Sources/Ligature/MockTextTokenizer.swift b/Sources/Ligature/MockTextTokenizer.swift
new file mode 100644
index 0000000..b5bc403
--- /dev/null
+++ b/Sources/Ligature/MockTextTokenizer.swift
@@ -0,0 +1,43 @@
+public final class MockTextTokenizer: TextTokenizer {
+	public enum Request: Hashable {
+		case position(Int, TextGranularity, TextDirection)
+	}
+
+	public enum Response: Hashable {
+		case position(Int?)
+		case rangeEnclosingPosition(Range<Int>?)
+	}
+
+	public private(set) var requests: [Request] = []
+	public var responses: [Response] = []
+
+	public init() {
+	}
+
+	public func closestMatchingVerticalLocation(to location: Int, above: Bool) -> Int? {
+		return nil
+	}
+
+	public func position(from position: Int, toBoundary granularity: TextGranularity, inDirection direction: TextDirection) -> Int? {
+		requests.append(.position(position, granularity, direction))
+
+		switch responses.removeFirst() {
+		case let .position(value):
+			return value
+		default:
+			fatalError("wrong return type")
+		}
+	}
+
+	public func rangeEnclosingPosition(_ position: Int, with granularity: TextGranularity, inDirection direction: TextDirection) -> Range<Int>? {
+		return nil
+	}
+
+	public func isPosition(_ position: Int, atBoundary granularity: TextGranularity, inDirection direction: TextDirection) -> Bool {
+		return false
+	}
+
+	public func isPosition(_ position: Int, withinTextUnit granularity: TextGranularity, inDirection direction: TextDirection) -> Bool {
+		return false
+	}
+}
diff --git a/Sources/Ligature/Platform.swift b/Sources/Ligature/Platform.swift
index 62ad02d..8b36e5f 100644
--- a/Sources/Ligature/Platform.swift
+++ b/Sources/Ligature/Platform.swift
@@ -1,7 +1,6 @@
-#if canImport(AppKit) && !targetEnvironment(macCatalyst)
+#if os(macOS)
 import AppKit
 
-@MainActor
 open class TextPosition: NSObject {
 
 }
@@ -191,6 +190,8 @@ extension NSTextSelection.Granularity {
 			self = .line
 		case .document:
 			self = .paragraph
+		@unknown default:
+			self = .character
 		}
 	}
 }
diff --git a/Sources/Ligature/SourceTokenizer.swift b/Sources/Ligature/SourceTokenizer.swift
index c95f453..d5c6933 100644
--- a/Sources/Ligature/SourceTokenizer.swift
+++ b/Sources/Ligature/SourceTokenizer.swift
@@ -1,6 +1,6 @@
 import Foundation
 
-public struct SourceTokenizer<Position, FallbackTokenzier: TextTokenizer> where FallbackTokenzier.Position == Position {
+public struct SourceTokenizer<Position, FallbackTokenzier: TextTokenizer> where FallbackTokenzier.Position == Position, FallbackTokenzier.TextRange == TextRange {
 	private let fallbackTokenzier: FallbackTokenzier
 
 	init(fallbackTokenzier: FallbackTokenzier) {
@@ -13,7 +13,7 @@ extension SourceTokenizer : TextTokenizer {
 		return fallbackTokenzier.position(from: position, toBoundary: granularity, inDirection: direction)
 	}
 
-	public func rangeEnclosingPosition(_ position: Position, with granularity: TextGranularity, inDirection direction: TextDirection) -> TextRange? {
+	public func rangeEnclosingPosition(_ position: Position, with granularity: TextGranularity, inDirection direction: TextDirection) -> Ligature.TextRange? {
 		return fallbackTokenzier.rangeEnclosingPosition(position, with: granularity, inDirection: direction)
 	}
 
diff --git a/Sources/Ligature/TextInputStringTokenizer.swift b/Sources/Ligature/TextInputStringTokenizer.swift
index 9cdcc4d..80a11f9 100644
--- a/Sources/Ligature/TextInputStringTokenizer.swift
+++ b/Sources/Ligature/TextInputStringTokenizer.swift
@@ -1,5 +1,5 @@
 import Foundation
-#if canImport(AppKit) && !targetEnvironment(macCatalyst)
+#if os(macOS)
 import AppKit
 
 extension NSTextView {
diff --git a/Sources/Ligature/TextTokenizer.swift b/Sources/Ligature/TextTokenizer.swift
index 51582fb..805eca9 100644
--- a/Sources/Ligature/TextTokenizer.swift
+++ b/Sources/Ligature/TextTokenizer.swift
@@ -1,8 +1,9 @@
 import Foundation
 
 @MainActor
-public protocol TextTokenizer<Position> {
-	associatedtype Position : TextPosition
+public protocol TextTokenizer<Position, TextRange> {
+	associatedtype Position
+	associatedtype TextRange
 
 	func position(from position: Position, toBoundary granularity: TextGranularity, inDirection direction: TextDirection) -> Position?
 	func rangeEnclosingPosition(_ position: Position, with granularity: TextGranularity, inDirection direction: TextDirection) -> TextRange?