test: add tests for InteractionOutput class

test/core/interaction_output_test.dart

@@ -0,0 +1,59 @@
+// 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/content.dart';
+import 'package:dart_wot/src/core/content_serdes.dart';
+import 'package:dart_wot/src/core/interaction_output.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('InteractionOutput should', () {
+    test('output the correct value', () async {
+      const inputValue = 'foo';
+      final input = utf8.encode(inputValue);
+
+      final contentSerdes = ContentSerdes();
+      final content = Content(
+        'text/plain',
+        Stream.fromIterable([
+          input,
+        ]),
+      );
+
+      final interactionOutput = InteractionOutput(content, contentSerdes);
+
+      final value1 = await interactionOutput.value();
+      expect(value1, inputValue);
+
+      // Should return the same value
+      final value2 = await interactionOutput.value();
+      expect(value2, inputValue);
+    });
+
+    test('output the same value when calling value() twice', () async {
+      const inputValue = 'bar';
+      final input = utf8.encode(inputValue);
+
+      final contentSerdes = ContentSerdes();
+      final content = Content(
+        'text/plain',
+        Stream.fromIterable([
+          input,
+        ]),
+      );
+
+      final interactionOutput = InteractionOutput(content, contentSerdes);
+
+      final value1 = await interactionOutput.value();
+      expect(value1, inputValue);
+
+      final value2 = await interactionOutput.value();
+      expect(value1, value2);
+    });
+  });
+}