public async Task RipFile() { // Give var operatingSystemLayer = Substitute.For <IOperatingSystemLayer>(); var configService = Substitute.For <IConfigService>(); configService .Config() .Returns(new JsonConfig()); var fileRipper = new FileRipper(operatingSystemLayer, configService); // When await fileRipper.RipFile("fileName"); // Then await operatingSystemLayer.Received(1).CreatePath(Arg.Any <string>()); await operatingSystemLayer.Received(1).CopyFile(Arg.Any <string>(), Arg.Any <string>()); }