[platform_channels] adds EventChannel Demo (#462)

platform_channels/test/src/event_channel_demo_test.dart

@@ -0,0 +1,73 @@
+// Copyright 2020 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:platform_channels/src/event_channel_demo.dart';
+
+void main() {
+  group('EventChannel Demo tests', () {
+    final sensorValues = [1.3556, 2.3, -0.12];
+    setUpAll(() {
+      // By default EventChannel uses StandardMethodCodec to communicate with
+      // platform.
+      const standardMethod = StandardMethodCodec();
+
+      // This function handles the incoming messages from the platform. It
+      // calls the BinaryMessenger.setMessageHandler registered for the EventChannel
+      // and add the incoming message to the StreamController used by the EventChannel
+      // after decoding the message with codec used by the EventChannel.
+      void emitValues(ByteData event) {
+        ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage(
+          'eventChannelDemo',
+          event,
+          (reply) {},
+        );
+      }
+
+      // Register a mock for EventChannel. EventChannel under the hood uses
+      // MethodChannel to listen and cancel the created stream.
+      ServicesBinding.instance.defaultBinaryMessenger
+          .setMockMessageHandler('eventChannelDemo', (message) async {
+        // Decode the message into MethodCallHandler.
+        final methodCall = standardMethod.decodeMethodCall(message);
+
+        if (methodCall.method == 'listen') {
+          // Emit new sensor values.
+          emitValues(standardMethod.encodeSuccessEnvelope(sensorValues));
+          emitValues(null);
+          return standardMethod.encodeSuccessEnvelope(null);
+        } else if (methodCall.method == 'cancel') {
+          return standardMethod.encodeSuccessEnvelope(null);
+        } else {
+          fail('Expected listen or cancel');
+        }
+      });
+    });
+
+    testWidgets('EventChannel AccelerometerReadings Stream test',
+        (tester) async {
+      await tester.pumpWidget(MaterialApp(
+        home: EventChannelDemo(),
+      ));
+
+      await tester.pumpAndSettle();
+
+      // Check the values of axis. The value is rounded to 3 decimal places.
+      expect(
+        find.text('x axis: ' + sensorValues[0].toStringAsFixed(3)),
+        findsOneWidget,
+      );
+      expect(
+        find.text('y axis: ' + sensorValues[1].toStringAsFixed(3)),
+        findsOneWidget,
+      );
+      expect(
+        find.text('z axis: ' + sensorValues[2].toStringAsFixed(3)),
+        findsOneWidget,
+      );
+    });
+  });
+}