Usage of ThreadStatic (Unit Testing)

Question

I have written the following to stub a Singleton for the purpose of unit testing.

 public static class LocalisationSetter
    {
        [ThreadStatic]
        private static CultureInfo _cultureInfo;

        public static void Set(CultureInfo cultureInfo)
        {
            _cultureInfo = cultureInfo;

            Localisation.Current.Culture = _cultureInfo; // Setting The singleton.
        }
    }

In my test I do something like below:

LocalisationSetter.Set(new CultureInfo("fr-FR"));

The above method just seems little "dirty"...

Just wondered if there is potentially a better way. I need to make sure the changes to "Localisation" is only visible to the thread.

Correct me if I'm wrong, but if Localisation.Current is not ThreadStatic also then your Setter class is pointless. Even if it is, the class doesn't do anything that you couldn't do straight from the test. — D Stanley
– D Stanley, Commented Mar 10, 2014 at 22:24
Can you clarify if there's something about this that is specific to unit testing? — Andrew Theken
– Andrew Theken, Commented Mar 10, 2014 at 22:30
Is there a particular reason you don't just set the thread's current culture? That is Thread.CurrentCulture = cultureInfo; Also Thread.CurrentUICulture. — Jim Mischel
– Jim Mischel, Commented Mar 11, 2014 at 2:54

Andrew Theken · Accepted Answer · 2014-03-10 22:41:03Z

3

Having a class that is a "Setter" is a fairly peculiar pattern. As DStanley commented, the above will not work as expected without Making Localization.Current thread-static, too:

public class Localization{

   [ThreadStatic]
   private static Localization _current;

   public static Current {
     get { _current = _current ?? new Localization(); return _current }
     set { _current = value; }
   }
}

That being said, this is generally a very peculiar pattern, as this is effectively creating "global" variables, which generally makes unit testing, and software maintenance more complicated.

(The above code creates ephemeral state that could change at any time, impacting the behavior of your code).

Consider using dependency injection, or at a minimum, organizing these "global" variables into a few aggregate objects so that the fact that you do have these context objects around is easier to track.

answered Mar 10, 2014 at 22:41

Andrew Theken

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2 Comments

msuhash Over a year ago

I thought if the "global" refers to a thread static instance then each thread will get its own copy. This way each test can run in isolation. Thanks!

Andrew Theken Over a year ago

@msuhash, It's true that ThreadStatic will isolate this per thread, but the point of my answer was that you're creating shared state and not passing it via normal conventions (i.e. method calls/passing objects). This is probably a code smell, and should be avoided.

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