TF-1233 Fix error out of range in create avatar icon

core/test/presentation/extensions/string_extension_test.dart

@@ -0,0 +1,61 @@
+import 'package:core/presentation/extensions/string_extension.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group("firstLetterToUpperCase()", () {
+    test("from 2 digits number", () {
+      const twentyThree = '23';
+      expect(twentyThree.firstLetterToUpperCase, equals('23'));
+    });
+
+    test("from 3 digits number", () {
+      const twentyThreeThree = '233';
+      expect(twentyThreeThree.firstLetterToUpperCase, equals('23'));
+    });
+
+    test("from 1 digit number", () {
+      const two = '2';
+      expect(two.firstLetterToUpperCase, equals('2'));
+    });
+
+    test("from 1 character", () {
+      const two = 'A';
+      expect(two.firstLetterToUpperCase, equals('A'));
+    });
+
+    test("from name with multiple words", () {
+      const name = 'Grant big';
+      expect(name.firstLetterToUpperCase, equals('GB'));
+    });
+
+    test("from name with one word", () {
+      const name = 'Grant';
+      expect(name.firstLetterToUpperCase, equals('GR'));
+    });
+
+    test("from name mix with number and word", () {
+      const name = '23 Grant';
+      expect(name.firstLetterToUpperCase, equals('GG'));
+    });
+
+    test("from name mix with word and number", () {
+      const name = 'Grant 23';
+      expect(name.firstLetterToUpperCase, equals('GG'));
+    });
+
+    test("from empty string", () {
+      const name = '';
+      expect(name.firstLetterToUpperCase, equals(''));
+    });
+
+    test("from special string", () {
+      const name = '&^%';
+      expect(name.firstLetterToUpperCase, equals('&^'));
+    });
+
+    test("from multiple special string", () {
+      const name = '&^% *()^';
+      expect(name.firstLetterToUpperCase, equals(''));
+    });
+  });
+}