Krzysztof Koźmic's blog

Quick ques­tion – from the top of your head, with­out run­ning the code, what is the result of:

var foo = -00.053200000m;
var result = foo.ToString("##.##");

Or a dif­fer­ent one:

var foo = "foo";
var bar = "bar";
var foobar = "foo" + "bar";
var concaternated = new StringBuilder(foo).Append(bar).ToString(); 

var result1 = AreEqual(foobar, concaternated);
var result2 = Equals(foobar, concaternated);

public static bool AreEqual(object one, object two)
{
    return one == two;
}

How about this one from NHibernate?

var parent = session.Get<Parent>(1); 

DoSomething(parent.Child.Id); 

var result = NHibernateUtil.IsInitialized(parent.Child);

The point being?

Well, if you can answer all of the above with­out run­ning the code, we’re hir­ing. I don’t, and I sus­pect most peo­ple don’t either. That’s fine. Ques­tion is – what are you going to do about it? What do you do when some 3^rd party library, or part of stan­dard library exhibits unex­pected behav­iour? How do you go about learn­ing if what you think should hap­pen, is really what does happen?

Scratch­pad

I’ve seen peo­ple open up Visual Stu­dio, cre­ate ConsoleApplication38, write some code using the API in ques­tion includ­ing plenty of Console.WriteLine along the way (curse who­ever decided Client Pro­file should be the default for Con­sole appli­ca­tions, switch to full .NET pro­file) com­pile, run and dis­card the code. And then repeat the process with ConsoleApplication39 next time.

The solu­tion I’m using feels a bit more light­weight, and has worked for me well over the years. It is very sim­ple – I lever­age my exist­ing test frame­work and test run­ner. I cre­ate an empty test fix­ture called Scratchpad.

This class gets com­mit­ted to the VCS repos­i­tory. That way every mem­ber of the team gets their own scratch­pad to play with and val­i­date their the­o­ries, ideas and assump­tions. How­ever, as the name implies, this all is a one-off throw­away code. After all, you don’t really need to test the BCL. One would hope Microsoft already did a good job at that.

If you’re using git, you can eas­ily tell it not to track changes to the file, by run­ning the fol­low­ing com­mand (after you com­mit the file):

git update-index –assume-unchanged Scratchpad.cs

With this sim­ple set up you will have quick place to val­i­date your assump­tions (and answer ques­tions about API behav­iour) with lit­tle friction.

So there you have it, a new, use­ful tech­nique in your toolbelt.