public void GetCurrentLogReturnsString() { //Arrange var mockUow = new Mock <IUnitOfWork>(); mockUow.Setup(a => a.Orders.GetAll()).Returns(new List <Order>()); //Act var service = new RentService(mockUow.Object); var result = service.GetCurrentLog("somePath"); //Assert Assert.That(result, Is.TypeOf(typeof(string))); }