Add test demonstrating getServices support for multiple registrations

test_multiple_singletons.dart

@@ -0,0 +1,56 @@
+import 'package:extensions/dependency_injection.dart';
+
+abstract class IService {
+  String getName();
+}
+
+class ServiceA implements IService {
+  @override
+  String getName() => 'ServiceA';
+}
+
+class ServiceB implements IService {
+  @override
+  String getName() => 'ServiceB';
+}
+
+class ServiceC implements IService {
+  @override
+  String getName() => 'ServiceC';
+}
+
+void main() {
+  print('Testing multiple addSingleton calls...\n');
+
+  // Create a service collection and register multiple services of the same type
+  final services = ServiceCollection()
+    ..addSingleton<IService>((_) => ServiceA())
+    ..addSingleton<IService>((_) => ServiceB())
+    ..addSingleton<IService>((_) => ServiceC());
+
+  // Build the service provider
+  final provider = services.buildServiceProvider();
+
+  // Test 1: Get single service (should return the last registered)
+  final singleService = provider.getService<IService>();
+  print('Single service via getService<T>(): ${singleService?.getName()}');
+
+  // Test 2: Get all services
+  final allServices = provider.getServices<IService>();
+  print('\nAll services via getServices<T>():');
+  for (var service in allServices) {
+    print('  - ${service.getName()}');
+  }
+
+  print('\nTotal services registered: ${allServices.length}');
+
+  // Verify all three services are returned
+  final names = allServices.map((s) => s.getName()).toList();
+  assert(names.contains('ServiceA'), 'ServiceA not found');
+  assert(names.contains('ServiceB'), 'ServiceB not found');
+  assert(names.contains('ServiceC'), 'ServiceC not found');
+  assert(allServices.length == 3, 'Expected 3 services, got ${allServices.length}');
+
+  print('\n✓ All assertions passed!');
+  print('✓ Multiple addSingleton calls ARE supported and can be retrieved via getServices<T>()');
+}