Add unit tests

test/in_app_update_test.dart

@@ -0,0 +1,85 @@
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter_in_app_update/in_app_update.dart';
+
+/// Return value of checkForUpdate method channel with mock results.
+final checkUpdateChannelResult = {
+  'updateAvailability': 1,
+  'immediateAllowed': true,
+  'flexibleAllowed': false,
+  'availableVersionCode': 2,
+  'installStatus': 3,
+  'packageName': 'foo',
+  'clientVersionStalenessDays': 4,
+  'updatePriority': 5,
+};
+
+/// Mock return value of [InAppUpdate.checkForUpdate].
+///
+/// Assumes that method channel returns [checkUpdateChannelResult].
+final AppUpdateInfo checkUpdateResult =
+    AppUpdateInfo(1, true, false, 2, 3, 'foo', 4, 5);
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  const channel = MethodChannel('in_app_update');
+  final log = <MethodCall>[];
+
+  channel.setMockMethodCallHandler((MethodCall methodCall) async {
+    log.add(methodCall);
+    switch (methodCall.method) {
+      case 'checkForUpdate':
+        return checkUpdateChannelResult;
+      case 'performImmediateUpdate':
+        return null;
+      case 'startFlexibleUpdate':
+        return null;
+      default:
+        assert(false);
+        return null;
+    }
+  });
+
+  tearDown(() {
+    log.clear();
+  });
+
+  group('InAppUpdate.checkForUpdate', () {
+    test('invokes appropriate method channel.', () async {
+      await InAppUpdate.checkForUpdate();
+      expect(log, <Matcher>[isMethodCall('checkForUpdate', arguments: null)]);
+    });
+
+    test('returns correct result.', () async {
+      final result = await InAppUpdate.checkForUpdate();
+      expect(result, checkUpdateResult);
+    });
+  });
+
+  group('InAppUpdate.performImmediateUpdate', () {
+    test('invokes appropriate method channel.', () async {
+      await InAppUpdate.performImmediateUpdate();
+      expect(log,
+          <Matcher>[isMethodCall('performImmediateUpdate', arguments: null)]);
+    });
+
+    test('reports success.', () async {
+      final result = await InAppUpdate.performImmediateUpdate();
+      expect(result, AppUpdateResult.success);
+    });
+  });
+
+  group('InAppUpdate.startFlexibleUpdate', () {
+    test('invokes appropriate method channel.', () async {
+      await InAppUpdate.startFlexibleUpdate();
+      expect(
+          log, <Matcher>[isMethodCall('startFlexibleUpdate', arguments: null)]);
+    });
+
+    test('reports success.', () async {
+      final result = await InAppUpdate.startFlexibleUpdate();
+      expect(result, AppUpdateResult.success);
+    });
+  });
+}