test: add tests for codecs

test/core/codec_test.dart

@@ -0,0 +1,28 @@
+// Copyright 2023 Contributors to the Eclipse Foundation. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+//
+// SPDX-License-Identifier: BSD-3-Clause
+
+import 'dart:convert';
+
+import 'package:dart_wot/src/core/codecs/text_codec.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('TextCodec', () {
+    test('should convert bytes to values and back', () {
+      final textCodec = TextCodec();
+
+      const testValue = 'foo';
+      final testInput = utf8.encode(testValue);
+
+      final convertedValue = textCodec.bytesToValue(testInput, null, {});
+      expect(convertedValue?.value, testValue);
+
+      final convertedBytes = textCodec.valueToBytes(convertedValue, null, {});
+
+      expect(convertedBytes, testInput);
+    });
+  });
+}