implemented tests

test/resolvers/singelton_resolver_test.dart

@@ -0,0 +1,36 @@
+import 'package:dart_di/resolvers/factory_resolver.dart';
+import 'package:dart_di/resolvers/singelton_resolver.dart';
+import 'package:test/test.dart';
+import 'package:mockito/mockito.dart' as mockito;
+
+void main() {
+  test(
+      'Not singleton resolver resolves different values after multiple resolve() calls',
+      () {
+    const callCount = 3;
+    final spy = new SpyMock();
+    final factoryResolver = new FactoryResolver(() => spy..onFactory());
+
+    for (var i = 0; i < callCount; i++) factoryResolver.resolve();
+
+    mockito.verify(spy.onFactory()).called(callCount);
+  });
+
+  test('Singleton resolver resolves same value after multiple resolve() calls',
+      () {
+    const callCount = 3;
+    final spy = new SpyMock();
+    final singletonResolver =
+        new SingletonResolver(new FactoryResolver(() => spy..onFactory()));
+
+    for (var i = 0; i < callCount; i++) singletonResolver.resolve();
+
+    mockito.verify(spy.onFactory()).called(1);
+  });
+}
+
+abstract class Spy {
+  void onFactory();
+}
+
+class SpyMock extends mockito.Mock implements Spy {}