implement isString validator tests

Author: ArturAssisComp

lib/new_api_prototype/core_validators/required_validators.dart

@@ -4,10 +4,10 @@ import '../constants.dart';
 /// This function generates a validator that enforces a required field rule. If
 /// the input is not provided (i.e., null or empty), the function returns an
 /// error message indicating that the field is required. If the input is
-/// provided, the function applies an additional validator v (if supplied) to
+/// provided, the function applies an additional validator `next` (if supplied) to
 /// further validate the input.
 Validator<T?> isRequired<T extends Object>([
-  Validator<T>? v,
+  Validator<T>? next,
   String? isRequiredMsg,
 ]) {
   String? finalValidator(T? value) {
@@ -17,7 +17,7 @@ Validator<T?> isRequired<T extends Object>([
       return isRequiredMsg ??
           FormBuilderLocalizations.current.requiredErrorText;
     }
-    return v?.call(transformedValue!);
+    return next?.call(transformedValue!);
   }
 
   return finalValidator;
@@ -37,10 +37,10 @@ String errorIsOptionalTemporary(String vErrorMessage) {
 /// This function generates a validator that marks a field as optional. If the
 /// user input is not provided (i.e., it's null or empty), the validator will
 /// return null, indicating no validation error. If the input is provided, the
-/// function applies an additional validator v (if provided) to further validate
+/// function applies an additional validator `next` (if provided) to further validate
 /// the input.
 Validator<T?> isOptional<T extends Object>([
-  Validator<T>? v,
+  Validator<T>? next,
   String Function(String)? isOptionalMsg,
 ]) {
   String? finalValidator(T? value) {
@@ -50,7 +50,7 @@ Validator<T?> isOptional<T extends Object>([
       // field not provided
       return null;
     }
-    final String? vErrorMessage = v?.call(transformedValue!);
+    final String? vErrorMessage = next?.call(transformedValue!);
     if (vErrorMessage == null) {
       return null;
     }

lib/new_api_prototype/core_validators/type_validators.dart

@@ -3,14 +3,23 @@
 import '../../localization/l10n.dart';
 import '../constants.dart';
 
-Validator<T> isString<T extends Object>(Validator<String>? v,
-    {String? isStringMsg}) {
+const tmpIsStringMsg = 'This field requires a valid string.';
+
+/// This function returns a validator that checks if the user input is a `String`.
+/// If it is a `String`, then it returns null when `next` is not provided. Otherwise,
+/// if `next` is provided, it passes the transformed value as `String` to the `next`
+/// validator.
+Validator<T> isString<T extends Object>([
+  Validator<String>? next,
+  String? isStringMsg,
+]) {
   String? finalValidator(T value) {
-    final (isValid, typeTransformedValue) = _isStringValidateAndConvert(value);
+    final (bool isValid, String? typeTransformedValue) =
+        _isStringValidateAndConvert(value);
     if (!isValid) {
-      return isStringMsg ?? 'This field requires a valid string.';
+      return isStringMsg ?? tmpIsStringMsg;
     }
-    return v?.call(typeTransformedValue!);
+    return next?.call(typeTransformedValue!);
   }
 
   return finalValidator;

test/new_api_testing/core_validators/type_validators_test.dart

@@ -0,0 +1,36 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:form_builder_validators/form_builder_validators.dart';
+
+void main() {
+  const String errorMsg = 'error msg';
+  String? hasLengthGreaterThan3(String input) =>
+      input.length > 3 ? null : errorMsg;
+
+  group('Validator: isString', () {
+    test('Should only check if the input is a String', () {
+      final Validator<Object> v = isString();
+
+      expect(v(123), equals(tmpIsStringMsg));
+      expect(v('123'), isNull);
+      expect(v('1'), isNull);
+      expect(v(''), isNull);
+    });
+    test('Should check if the input is a String with length greater than 3',
+        () {
+      final Validator<Object> v = isString(hasLengthGreaterThan3);
+
+      expect(v(123), equals(tmpIsStringMsg));
+      expect(v('1234'), isNull);
+      expect(v('12'), errorMsg);
+      expect(v(''), errorMsg);
+    });
+    test('Should check if the input is a String with using custom error', () {
+      const String customError = 'custom error';
+      final Validator<Object> v = isString(null, customError);
+
+      expect(v(123), equals(customError));
+      expect(v('1234'), isNull);
+      expect(v('12'), isNull);
+    });
+  });
+}