implement debug print validator

Author: ArturAssisComp

lib/new_api_prototype/core_validators/debug_print_validator.dart

@@ -0,0 +1,18 @@
+import 'package:flutter/widgets.dart';
+
+import '../constants.dart';
+
+/// Each time the user provides an `input`, this validator prints its [String]
+/// representation to `stdout` for debugging purposes.
+///
+/// The logging message can be customized providing the `logOnInput` parameter.
+///
+/// If the validator `next` is provided, it redirects user's input to it, returning
+/// its result. Otherwise, it never fails, thus, always returning `null`.
+Validator<T> debugPrintValidator<T extends Object?>(
+    {Validator<T>? next, String Function(T)? logOnInput}) {
+  return (T value) {
+    debugPrint(logOnInput?.call(value) ?? value.toString());
+    return next?.call(value);
+  };
+}

test/new_api_testing/core_validators/debug_print_validator_test.dart

@@ -0,0 +1,67 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:form_builder_validators/new_api_prototype/constants.dart';
+import 'package:form_builder_validators/new_api_prototype/core_validators/debug_print_validator.dart';
+
+class _CustomClass {
+  @override
+  String toString() => 'this is a string';
+}
+
+void main() {
+  group('Validator: debugPrintValidator', () {
+    final List<({String objectDescription, Object? value})> testCases =
+        <({String objectDescription, Object? value})>[
+      (objectDescription: 'empty string', value: ''),
+      (objectDescription: 'null', value: null),
+      (objectDescription: 'custom class', value: _CustomClass()),
+      (objectDescription: 'string \'input 1\'', value: 'input 1'),
+    ];
+    for (final (objectDescription: String dsc, value: Object? value)
+        in testCases) {
+      test('Should print the String representation for: $dsc', () {
+        final Validator<Object?> v = debugPrintValidator();
+        expect(() => v(value), prints(equals('$value\n')));
+        expect(v(value), isNull);
+      });
+    }
+
+    test(
+        'Should print the String representation of the input with next validator',
+        () {
+      const String errorMsg = 'error msg';
+      final Validator<Object?> v = debugPrintValidator(
+          next: (Object? v) => v is int && v % 2 == 0 ? null : errorMsg);
+
+      expect(() => v(13), prints(equals('13\n')),
+          reason: 'check stdout when input is \'13\'');
+      expect(v(13), errorMsg,
+          reason: 'check return value when input is \'13\'');
+
+      expect(() => v('not int'), prints(equals('not int\n')),
+          reason: 'check stdout when input is \'not int\'');
+      expect(v('not int'), errorMsg,
+          reason: 'check return value when input is \'not int\'');
+
+      expect(() => v(10), prints(equals('10\n')),
+          reason: 'check stdout when input is \'10\'');
+      expect(v(10), isNull, reason: 'check return value when input is \'10\'');
+    });
+    test('Should print the custom String representation of the input', () {
+      String logOnInput(Object? v) {
+        return 'Hello world $v';
+      }
+
+      final Validator<Object?> v = debugPrintValidator(logOnInput: logOnInput);
+
+      expect(() => v(13), prints(equals('${logOnInput(13)}\n')),
+          reason: 'check stdout when input is \'13\'');
+      expect(v(13), isNull, reason: 'check return value when input is \'13\'');
+
+      final _CustomClass c = _CustomClass();
+      expect(() => v(c), prints(equals('${logOnInput(c)}\n')),
+          reason: 'check stdout when input is a custom object');
+      expect(v(c), isNull,
+          reason: 'check return value when input is a custom object');
+    });
+  });
+}