public void M_WillAppendAllRowsInCsvFileToSpecifiedWorksheet() { // Arrange var sheet_name = "MockSheet"; var mock_file_io = new Mock <IFileIO <BankRecord> >(); mock_file_io.Setup(x => x.Load(It.IsAny <List <string> >(), null)) .Returns(new List <BankRecord>()); var csv_file = new CSVFile <BankRecord>(mock_file_io.Object); csv_file.Load(); var mock_spreadsheet_repo = new Mock <ISpreadsheetRepo>(); mock_spreadsheet_repo.Setup(x => x.Append_csv_file <BankRecord>(sheet_name, csv_file)) .Verifiable(); var spreadsheet = new Spreadsheet(mock_spreadsheet_repo.Object); // Act spreadsheet.Append_csv_file <BankRecord>(sheet_name, csv_file); // Clean up mock_spreadsheet_repo.Verify(x => x.Append_csv_file <BankRecord>(sheet_name, csv_file), Times.Once); }