implemented tests

test/resolvers/factory_resolver_test.dart

@@ -0,0 +1,27 @@
+import 'package:dart_di/resolvers/factory_resolver.dart';
+import 'package:test/test.dart';
+import 'package:mockito/mockito.dart' as mockito;
+
+void main() {
+  test('Factory resolver resolves with factory', () {
+    const expected = 3;
+    final factoryResolver = new FactoryResolver(() => expected);
+
+    expect(factoryResolver.resolve(), expected);
+  });
+
+  test('Factory creates value only after resolve() call', () {
+    final spy = new SpyMock();
+    final factoryResolver = new FactoryResolver(() => spy.onFactory());
+
+    mockito.verifyNever(spy.onFactory());
+    factoryResolver.resolve();
+    mockito.verify(spy.onFactory());
+  });
+}
+
+abstract class Spy {
+  void onFactory();
+}
+
+class SpyMock extends mockito.Mock implements Spy {}