public void ReaderMustReturnOk() { var fakeFileContents = "Id,Person,Population,Test \n 1,2,3,4"; byte[] fakeFileBytes = Encoding.UTF8.GetBytes(fakeFileContents); var fakeStream = new MemoryStream(fakeFileBytes); mockFileManager .Setup(f => f.GetStreamReader(It.IsAny <string>())) .Returns(() => new StreamReader(fakeStream)); var arg1 = "1"; var arg2 = "first.csv"; var arg3 = "Id"; var table = reader.ConvertCSVtoDataTable(arg1, arg2, arg3); Assert.IsTrue(table.PrimaryKey.FirstOrDefault().ColumnName == "Id"); Assert.IsTrue(table.Rows.Count == 1); Assert.IsTrue(table.Columns.Count == 4); }