add a loadContextsIntegration test

flutter/test/load_contexts_integrations_test.dart

@@ -0,0 +1,67 @@
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:mockito/mockito.dart';
+import 'package:sentry/sentry.dart';
+import 'package:sentry_flutter/sentry_flutter.dart';
+
+import 'mocks.dart';
+
+class MockTransport extends Mock implements Transport {}
+
+void main() {
+  const MethodChannel _channel = MethodChannel('sentry_flutter');
+
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  bool called = false;
+
+  setUp(() {
+    _channel.setMockMethodCallHandler((MethodCall methodCall) async {
+      called = true;
+      return {
+        'integrations': ['NativeIntegration'],
+        'package': {'sdk_name': 'native-package', 'version': '1.0'},
+        'contexts': {
+          'device': {'name': 'Device1'},
+          'app': {'app_name': 'test-app'},
+          'os': {'name': 'os1'},
+          'gpu': {'name': 'gpu1'},
+          'browser': {'name': 'browser1'},
+          'runtime': {'name': 'RT1'},
+          'theme': 'material',
+        }
+      };
+    });
+  });
+
+  tearDown(() {
+    _channel.setMockMethodCallHandler(null);
+  });
+
+  test('should apply the loadContextsIntegration eventProcessor', () async {
+    final options = SentryOptions()..dsn = fakeDsn;
+    final hub = Hub(options);
+
+    loadContextsIntegration(options, _channel)(hub, options);
+
+    expect(options.eventProcessors.length, 1);
+
+    final e = SentryEvent();
+    final event = await options.eventProcessors.first(e, null);
+
+    expect(called, true);
+    expect(event.contexts.device.name, 'Device1');
+    expect(event.contexts.app.name, 'test-app');
+    expect(event.contexts.operatingSystem.name, 'os1');
+    expect(event.contexts.gpu.name, 'gpu1');
+    expect(event.contexts.browser.name, 'browser1');
+    expect(
+        event.contexts.runtimes.any((element) => element.name == 'RT1'), true);
+    expect(event.contexts['theme'], 'material');
+    expect(
+      event.sdk.packages.any((element) => element.name == 'native-package'),
+      true,
+    );
+    expect(event.sdk.integrations.contains('NativeIntegration'), true);
+  });
+}