Sometimes, TDD doesn’t flow

I have been using test-driven development since I read Kent Beck’s book on the topic. I loved the book, I tried it, and adopted it, simply because it makes my life easier. It helps me think through what I am trying to achieve, and I like the safety net of having a test suite which tells me exactly what I have broken. It also fits well with the type of code I write, which is usually math-oriented, with nice, tight domain objects.

So when I decided recently to write a C# implementation of the Simplex algorithm, a classic method to resolve linear programming optimization problems, I expected a walk in the park.

(Side note:I am aware that re-implementing the Simplex is pointless, I am doing this as an exercise/experiment)

Turns out, I was mistaken. I have been struggling with this project pretty much from the beginning, and unit testing hasn’t really helped so far. Unfortunately, I didn’t reach a point where I fully understand what it is that is not flowing, but I decided I would share some of the problems I encountered. Maybe brighter minds than me can help me see what I am doing wrong!

Two level horizontal menu for ASP.NET

When I decided to have a 2-level horizontal menu for my professional webpage in ASP.NET, it came as a surprise to me that this wasn’t completely straightforward. I expected the standard  ASP menu control to support this, but found out that this wasn’t the case.

Fortunately, I came across a post by Peter Kellner, describing how he implemented that for the Silicon Valley Code Camp website, which was pretty much what I envisioned.

The one issue I had with his implementation, however, was that the second level menu uses multiple data sources. The Master Page handles the top-level menu, but each page contains a reference to the specific datasource used to populate the sub-menu. As a result, if you decide to add a page, you need to manually add to that page some code to define what sub-menu should show up, which is cumbersome.

The ideal solution for a lazy developer like me would be to have all the menus handled in the Master Page, so that when you add a new page to your website, you just need to add it to the Sitemap, and the right menu and sub-menu shows up.

Excel ScatterPlot with labels, colors and markers

Recently, a client asked me if it was possible to create an Excel scatter plot of his products, adding a label on each data point, and using different colors and symbols for different types of products. You could think of this as plotting 5 dimensions at once, instead of the usual two.

I quickly coded a VBA macro to do that, with a sample workbook to illustrate the usage. The macro is pretty rough, but was sufficient for my needs as is, so I haven’t put extra efforts in: feel free to improve upon it…

Here is a sample of the output:

Read the contents of a worksheet with C#

When working with Excel workbooks with C#, I often need to retrieve the entire contents of a particular worksheet, so that I can process the data within C# code. By “the entire contents”, I mean the content of every cell between cell A1 and the last cell of the sheet, that is, the cell such that there is no cell on its right or below it that contains anything.

To do this, I use the following code, where excelWorksheet is a Worksheet (duh):

Excel.Range firstCell = excelWorksheet.get_Range("A1", Type.Missing);
Excel.Range lastCell = excelWorksheet.Cells.SpecialCells(Excel.XlCellType.xlCellTypeLastCell, Type.Missing);

object[,] cellValues;
object[,] cellFormulas;

Excel.Range worksheetCells = excelWorksheet.get_Range(firstCell, lastCell);
cellValues = worksheetCells.Value2 as object[,];
cellFormulas = worksheetCells.Formula as object[,];

The 2 resulting arrays of objects, cellValues and cellFormulas, contain the values and formulas, or null if the cell has no content.

However, while I was working on Akin recently, I realized 2 interesting things I had never noted before. First, the resulting array is 1-based, even though “C# arrays are zero indexed; that is, the array indexes start at zero”. Then, this code will fail if your spreadsheet contains only one value, in cell A1.

The Art of Unit Testing

I recently finished reading the Art of Unit Testing, by Roy Osherove (Manning); here are a few thoughts on the book.

Who to give it too

This is an excellent book for the C# developer with solid foundations in object-oriented design, who has already some exposure to writing unit tests. If you have worked on a decent-scale project, and found yourself thinking “hmmm, I am sure there is a smarter way to write these tests”, you should definitely get that book. Note that while it will be extremely useful to the test-driven development practitioner, this is NOT a book on TDD.