TF-4169 Add precheck for HexColor and unit test

labels/lib/model/hex_color.dart

@@ -1,9 +1,24 @@
 import 'package:equatable/equatable.dart';
+import 'package:quiver/check.dart';
 
 class HexColor with EquatableMixin {
+  // Only accept #RRGGBB or #AARRGGBB format
+  static final RegExp _hexPattern =
+      RegExp(r'^#[0-9a-fA-F]{6}([0-9a-fA-F]{2})?$');
+
   final String value;
 
-  HexColor(this.value);
+  HexColor(this.value) {
+    checkArgument(value.isNotEmpty, message: 'hex string must not be empty');
+    checkArgument(
+      value.startsWith('#'),
+      message: 'hex string must start with #',
+    );
+    checkArgument(
+      _hexPattern.hasMatch(value),
+      message: 'invalid hex format: expected #RRGGBB or #AARRGGBB',
+    );
+  }
 
   @override
   List<Object> get props => [value];

labels/pubspec.lock

@@ -437,7 +437,7 @@ packages:
     source: hosted
     version: "1.4.0"
   quiver:
-    dependency: transitive
+    dependency: "direct main"
     description:
       name: quiver
       sha256: b1c1ac5ce6688d77f65f3375a9abb9319b3cb32486bdc7a1e0fdf004d7ba4e47

labels/pubspec.yaml

@@ -24,6 +24,8 @@ dependencies:
 
   dio: 5.0.0
 
+  quiver: 3.2.1
+
 dev_dependencies:
   flutter_test:
     sdk: flutter

labels/test/method/model/hex_color_test.dart

@@ -0,0 +1,71 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:labels/model/hex_color.dart';
+
+void main() {
+  group('HexColor', () {
+    test('creates instance when valid #RRGGBB', () {
+      final color = HexColor('#A1B2C3');
+      expect(color.value, '#A1B2C3');
+    });
+
+    test('creates instance when valid #AARRGGBB', () {
+      final color = HexColor('#80A1B2C3');
+      expect(color.value, '#80A1B2C3');
+    });
+
+    test('throws when value is empty', () {
+      expect(
+        () => HexColor(''),
+        throwsA(
+          predicate((e) =>
+              e is ArgumentError &&
+              e.message == 'hex string must not be empty'),
+        ),
+      );
+    });
+
+    test('throws when missing leading #', () {
+      expect(
+        () => HexColor('A1B2C3'),
+        throwsA(
+          predicate((e) =>
+              e is ArgumentError &&
+              e.message == 'hex string must start with #'),
+        ),
+      );
+    });
+
+    test('throws when format #FFF (unsupported)', () {
+      expect(
+        () => HexColor('#FFF'),
+        throwsA(
+          predicate((e) =>
+              e is ArgumentError &&
+              e.message == 'invalid hex format: expected #RRGGBB or #AARRGGBB'),
+        ),
+      );
+    });
+
+    test('throws when contains invalid characters', () {
+      expect(
+        () => HexColor('#GGHHII'),
+        throwsA(isA<ArgumentError>()),
+      );
+    });
+
+    test('throws when length is too long', () {
+      expect(
+        () => HexColor('#A1B2C3D4E5'),
+        throwsA(isA<ArgumentError>()),
+      );
+    });
+
+    test('supports value equality (Equatable)', () {
+      final c1 = HexColor('#FFFFFF');
+      final c2 = HexColor('#FFFFFF');
+
+      expect(c1, equals(c2));
+      expect(c1.props, equals(['#FFFFFF']));
+    });
+  });
+}