fix: improve email validation regex and enhance test coverage

lib/src/validations/valid_email_validation.dart

@@ -25,7 +25,7 @@ extension ValidEmailValidation on SimpleValidationBuilder<String> {
   SimpleValidationBuilder<String> validEmail({String? message, String? code}) {
     return useValidation(
       (value, entity) =>
-          RegExp(r'^[\w\.-]+@[a-zA-Z\d\.-]+\.[a-zA-Z]{2,}$').hasMatch(value),
+          RegExp(r'^[\w\.-]+@([A-Za-z0-9][A-Za-z0-9\-]*\.)+[A-Za-z]{2,}$').hasMatch(value),
       code: code ?? Language.code.validEmail,
       message: message,
     );
@@ -54,7 +54,7 @@ extension ValidEmailNullableValidation on SimpleValidationBuilder<String?> {
     return useValidation(
       (value, entity) =>
           value != null &&
-          RegExp(r'^[\w\.-]+@[a-zA-Z\d\.-]+\.[a-zA-Z]{2,}$').hasMatch(value),
+          RegExp(r'^[\w\.-]+@([A-Za-z0-9][A-Za-z0-9\-]*\.)+[A-Za-z]{2,}$').hasMatch(value),
       code: code ?? Language.code.validEmail,
       message: message,
     );
@@ -84,7 +84,7 @@ extension ValidEmailOrNullableValidation on SimpleValidationBuilder<String?> {
     return useValidation(
       (value, entity) =>
           value == null ||
-          RegExp(r'^[\w\.-]+@[a-zA-Z\d\.-]+\.[a-zA-Z]{2,}$').hasMatch(value),
+          RegExp(r'^[\w\.-]+@([A-Za-z0-9][A-Za-z0-9\-]*\.)+[A-Za-z]{2,}$').hasMatch(value),
       code: code ?? Language.code.validEmail,
       message: message,
     );

test/src/validations/valid_email_validation_test.dart

@@ -37,4 +37,24 @@ void main() {
 
     expect(result.isValid, true);
   });
+
+  test('valid email validation...', () {
+    final validator = TestLucidValidator<UserModel>();
+
+    validator
+        .ruleFor((e) => e.email, key: 'email', label: 'E-mail') //
+        .validEmail();
+
+    final user = UserModel()..email = 'test@.123.com';
+
+    final result = validator.validate(user);
+
+    expect(result.isValid, false);
+
+    expect(result.exceptions.length, 1);
+
+    final error = result.exceptions.first;
+
+    expect(error.message, "'E-mail' is not a valid email address.");
+  });
 }