implement is required validator

Author: ArturAssisComp

lib/new_api_prototype/core_validators/required_validators.dart

@@ -1,12 +1,19 @@
 import '../../localization/l10n.dart';
 import '../constants.dart';
 
-Validator<T?> isRequired<T extends Object>(
-  Validator<T>? v, {
+/// This function returns a transformer validator that checks if the user input
+/// is neither null nor empty, in the case it is a collection, a string or a map.
+/// If the condition was not satisfied, it returns the `isRequiredMsg` error message,
+/// if provided, or ´FormBuilderLocalizations.current.requiredErrorText´ otherwise.
+/// If the condition is satisfied, it returns the validation of the input with
+/// `v` or null if `v` was not provided.
+Validator<T?> isRequired<T extends Object>([
+  Validator<T>? v,
   String? isRequiredMsg,
-}) {
+]) {
   String? finalValidator(T? value) {
-    final (isValid, transformedValue) = _isRequiredValidateAndConvert(value);
+    final (bool isValid, T? transformedValue) =
+        _isRequiredValidateAndConvert(value);
     if (!isValid) {
       return isRequiredMsg ??
           FormBuilderLocalizations.current.requiredErrorText;
@@ -22,12 +29,13 @@ Validator<T?> isOptional<T extends Object>(
   String? isOptionalMsg,
 }) {
   String? finalValidator(T? value) {
-    final (isValid, transformedValue) = _isRequiredValidateAndConvert(value);
+    final (bool isValid, T? transformedValue) =
+        _isRequiredValidateAndConvert(value);
     if (!isValid) {
       // field not provided
       return null;
     }
-    final vErrorMessage = v?.call(transformedValue!);
+    final String? vErrorMessage = v?.call(transformedValue!);
     if (vErrorMessage == null) {
       return null;
     }

test/new_api_testing/core_validators/required_validators/is_required_validator_test.dart

@@ -0,0 +1,51 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:form_builder_validators/form_builder_validators.dart';
+
+const String errorMultBy6 = 'error';
+String? isMultipleBy6(int value) {
+  return value % 6 == 0 ? null : errorMultBy6;
+}
+
+void main() {
+  final String defaultError =
+      FormBuilderLocalizations.current.requiredErrorText;
+
+  group('Validator: isRequired', () {
+    test('Should check if the input value is not null/empty', () {
+      final Validator<Object?> v = isRequired();
+
+      expect(v(null), defaultError);
+      expect(v(''), defaultError);
+      expect(v(<String>[]), defaultError);
+      expect(v(<int, String>{}), defaultError);
+      expect(v(123), isNull);
+      expect(v(' '), defaultError);
+      expect(v('hello'), isNull);
+    });
+
+    test(
+        'Should check if the input value is not null/empty with composed validator `v`',
+        () {
+      final Validator<int?> v = isRequired(isMultipleBy6);
+
+      expect(v(null), equals(defaultError));
+      expect(v(0), isNull);
+      expect(v(1), equals(errorMultBy6));
+      expect(v(5), equals(errorMultBy6));
+      expect(v(6), isNull);
+    });
+
+    test('Should return custom message for null input', () {
+      const String customMsg = 'custom error message ';
+      final Validator<Object?> v = isRequired(null, customMsg);
+      final Validator<int?> v1 = isRequired(isMultipleBy6, customMsg);
+
+      expect(v(null), equals(customMsg));
+      expect(v(''), equals(customMsg));
+      expect(v1(null), equals(customMsg));
+      expect(v(0), isNull);
+      expect(v1(1), equals(errorMultBy6));
+      expect(v1(6), isNull);
+    });
+  });
+}