public async Task GetLatestData() { string numbers = "1 5 6"; string path = "file01.txt"; var mockFileService = new Mock <IFileService>(); mockFileService .Setup(f => f.ReadFromLastAvailableFile(It.IsAny <Stack <FileInfo> >())) .ReturnsAsync(new Tuple <string, string>(numbers, path)); var sortingService = new SortingService(mockFileService.Object); SavedData result = await sortingService.GetLatestData(); Assert.Equal(numbers, result.OrderedNumbers); Assert.Equal(path, result.FileName); }