diff --git a/test/features/public_asset/domain/extensions/string_to_public_asset_extension_test.dart b/test/features/public_asset/domain/extensions/string_to_public_asset_extension_test.dart
new file mode 100644
index 000000000..7dd13794e
--- /dev/null
+++ b/test/features/public_asset/domain/extensions/string_to_public_asset_extension_test.dart
@@ -0,0 +1,105 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:jmap_dart_client/jmap/core/id.dart';
+import 'package:tmail_ui_user/features/public_asset/domain/extensions/string_to_public_asset_extension.dart';
+
+void main() {
+  group('string to public asset extension test:', () {
+    test(
+      'should convert string to public assets '
+      'when image tags have public-asset-id attribute',
+    () {
+      // arrange
+      const publicAssetIdValue1 = 'public-asset-1';
+      const publicAssetIdValue2 = 'public-asset-2';
+      const htmlString = '<img src="public-asset-1" public-asset-id="$publicAssetIdValue1"/>'
+        '<img src="public-asset-2" public-asset-id="$publicAssetIdValue2"/>';
+
+      // act
+      final publicAssetIds = htmlString.publicAssetIdsFromHtmlContent;
+      
+      // assert
+      expect(publicAssetIds, equals([Id(publicAssetIdValue1), Id(publicAssetIdValue2)]));
+    });
+
+    test(
+      'should convert string to nothing '
+      'when image tags do not have public-asset-id attribute',
+    () {
+      // arrange
+      const htmlString = '<img src="public-asset-1"/><img src="public-asset-2"/>';
+
+      // act
+      final publicAssetIds = htmlString.publicAssetIdsFromHtmlContent;
+      
+      // assert
+      expect(publicAssetIds, isEmpty);
+    });
+
+    test(
+      'should only convert string to public assets '
+      'when image tags have public-asset-id attribute',
+    () {
+      // arrange
+      const publicAssetIdValue1 = 'public-asset-1';
+      const htmlString = '<img src="public-asset-1" public-asset-id="$publicAssetIdValue1"/>'
+        '<img src="public-asset-2"/>';
+
+      // act
+      final publicAssetIds = htmlString.publicAssetIdsFromHtmlContent;
+      
+      // assert
+      expect(publicAssetIds, equals([Id(publicAssetIdValue1)]));
+    });
+
+    group('should convert string to public assets in various edge cases:', () {
+      test(
+        'when there are two "public-asset-id" attributes in the same image tag',
+      () {
+        // arrange
+        const publicAssetIdValue1 = 'public-asset-1';
+        const publicAssetIdValue2 = 'public-asset-2';
+        const htmlString = '<img src="public-asset-1" '
+          'public-asset-id="$publicAssetIdValue1" '
+          'public-asset-id="$publicAssetIdValue2"/>';
+        
+        // act
+        final publicAssetIds = htmlString.publicAssetIdsFromHtmlContent;
+        
+        // assert
+        expect(publicAssetIds, equals([Id(publicAssetIdValue1)]));
+      });
+
+      test(
+        'only with the "public-asset-id" attribute name',
+      () {
+        // arrange
+        const publicAssetIdValue1 = 'public-asset-1';
+        const publicAssetIdValue2 = 'public-asset-2';
+        const htmlString = '<img src="public-asset-1" '
+          'public-at-id="$publicAssetIdValue1" '
+          'public-asset-id="$publicAssetIdValue2"/>';
+        
+        // act
+        final publicAssetIds = htmlString.publicAssetIdsFromHtmlContent;
+        
+        // assert
+        expect(publicAssetIds, equals([Id(publicAssetIdValue2)]));
+      });
+    });
+
+    test(
+      'should throw invalid argument exception '
+      'when the public asset id contains invalid characters',
+    () {
+      // arrange
+      const publicAssetIdValue1 = r'#$52323';
+      const htmlString = '<img src="public-asset-1" public-asset-id="$publicAssetIdValue1"/>';
+      
+      // assert
+      expect(
+        () => htmlString.publicAssetIdsFromHtmlContent,
+        throwsA(isA<ArgumentError>())
+      );
+    });
+  });
+}
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