Add tests for applyAttribute/applyAttributes helpers with emoji

Verify that applyAttribute, applyAttributes, and applyForegroundColor
correctly cover the full string length when the string contains
multi-byte characters like emoji.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jkmassel

Modules/Tests/WordPressUIUnitTests/Extensions/NSMutableAttributedStringHelpersTests.swift

@@ -0,0 +1,60 @@
+import Testing
+import UIKit
+
+@testable import WordPressUI
+
+struct NSMutableAttributedStringHelpersTests {
+
+    // MARK: - applyAttribute(_:value:)
+
+    @Test("applyAttribute covers the full string including emoji")
+    func applyAttributeWithEmoji() {
+        // 👨‍👩‍👧‍👦 is 1 grapheme cluster but 11 UTF-16 code units
+        let string = NSMutableAttributedString(string: "Hello 👨‍👩‍👧‍👦 World")
+        string.applyAttribute(.foregroundColor, value: UIColor.red)
+
+        var effectiveRange = NSRange()
+        let value = string.attribute(.foregroundColor, at: 0, effectiveRange: &effectiveRange)
+
+        #expect(value != nil)
+        #expect(effectiveRange.location == 0)
+        #expect(effectiveRange.length == string.length)
+    }
+
+    // MARK: - applyAttributes(_:)
+
+    @Test("applyAttributes covers the full string including emoji")
+    func applyAttributesWithEmoji() {
+        let string = NSMutableAttributedString(string: "👨‍👩‍👧‍👦👨‍👩‍👧‍👦 テスト")
+        let attrs: [NSAttributedString.Key: Any] = [
+            .foregroundColor: UIColor.blue,
+            .font: UIFont.systemFont(ofSize: 14)
+        ]
+        string.applyAttributes(attrs)
+
+        var colorRange = NSRange()
+        let color = string.attribute(.foregroundColor, at: 0, effectiveRange: &colorRange)
+
+        var fontRange = NSRange()
+        let font = string.attribute(.font, at: 0, effectiveRange: &fontRange)
+
+        #expect(color != nil)
+        #expect(colorRange.length == string.length)
+        #expect(font != nil)
+        #expect(fontRange.length == string.length)
+    }
+
+    // MARK: - applyForegroundColor(_:)
+
+    @Test("applyForegroundColor covers the full string including emoji")
+    func applyForegroundColorWithEmoji() {
+        let string = NSMutableAttributedString(string: "🌍 Hello 🌍")
+        string.applyForegroundColor(.green)
+
+        var effectiveRange = NSRange()
+        let value = string.attribute(.foregroundColor, at: 0, effectiveRange: &effectiveRange)
+
+        #expect(value as? UIColor == .green)
+        #expect(effectiveRange.length == string.length)
+    }
+}