adding in initial plugin code

test/multimedia_test.dart

@@ -0,0 +1,29 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:multimedia/multimedia.dart';
+import 'package:multimedia/multimedia_platform_interface.dart';
+import 'package:multimedia/multimedia_method_channel.dart';
+import 'package:plugin_platform_interface/plugin_platform_interface.dart';
+
+class MockMultimediaPlatform
+    with MockPlatformInterfaceMixin
+    implements MultimediaPlatform {
+
+  @override
+  Future<String?> getPlatformVersion() => Future.value('42');
+}
+
+void main() {
+  final MultimediaPlatform initialPlatform = MultimediaPlatform.instance;
+
+  test('$MethodChannelMultimedia is the default instance', () {
+    expect(initialPlatform, isInstanceOf<MethodChannelMultimedia>());
+  });
+
+  test('getPlatformVersion', () async {
+    Multimedia multimediaPlugin = Multimedia();
+    MockMultimediaPlatform fakePlatform = MockMultimediaPlatform();
+    MultimediaPlatform.instance = fakePlatform;
+
+    expect(await multimediaPlugin.getPlatformVersion(), '42');
+  });
+}